You can purge memory in Terminal for free. But this is a neat free app from well-known dev Rocky Sand Studio, showing your memory usage and allowing you to ‘Recycle Memory’ - and even have the app do it automatically:
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I didn’t know that about Terminal - that’s pretty cool. 
And Memory Diag is a super-slick little app. Even knowing how to do it in Terminal, it’s cool to have a little dashboard that shows what’s going on overall.
I really do not trust CleanMyMac, and would warn people to look very carefully at what it is going to do, because I think it will eventually break legit apps if not used with caution.
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In my opinion, freeing memory isn’t something we need to do. Just like cycling batteries isn’t needed.
The XNU/Mach/BSD kernel has sophisticated memory management built in. When an application needs more memory, the kernel will take care of spooling to swap, or freeing unused memory.
Why do you think that?
I can tell you that I’ve had a couple of times where I’ve had 32 GB of RAM full and 10 GB of swap space used, with (presently) relatively light system load. I think there were some Chrome things that went off the rails and just kept gobbling RAM.
Freeing memory with CleanMyMac actually did solve the problem.
But those are rare. It’s the sort of thing where I like having the tool to do it, but where I don’t break out the tool all that often. 
That really isn’t true, especially when your system repeatedly fills up RAM and thus slows down your system by saving to disk. Many apps leak RAM too and it’s easier to clean up RAM than quit and relaunch. I have 40Gb RAM and usually have a few dozen tabs open - using an extension that “sleeps” tabs not visited after x minutes recoups RAM in Brave, but Safari can still suck up ridiculous amounts.
Edit: I recently wrote about this (with screenshots) here.
What’s the extension you use for that?
The Great Suspender. It’s one of the most used and highly-rated Chromium extensions.
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My Mac is good at not crashing when RAM fills, but I regularly use it with immediate, very noticeable, positive effect on my 16GB machine. It slows down to a crawl at times.
My 32GB machine has no such problems.
This is only when multitasking with apps like Final Cut, XCode, Chrome (bonkers to me that a web browser is in that list) and I know how to avoid it happening, but I prefer to push my machine to work how I want it to and clearing RAM lets me do that.
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I was experiencing that too with 16Gb RAM, but in situations that aren’t uncommon for me I experience them with my current 40Gb RAM as well. I currently have six apps open, and two dozen menubar utilities, and 49 tabs open in Brave (most RAM-suspended) and 15 tabs open in Safari. 40Gb RAM installed and this is my current RAM situation:
If I hadn’t auto-suspended those Brave tabs (I’ve got a backlog of 6 unwatched YouTube videos alone that would have eaten up RAM in preload) I’d have been left with less than 4Gb RAM and a lot of data would have been written to disk, which, in combination with reading from disk to retrieve it would have made the Mac decidedly sluggish.
Add in the fact that Chrome and Chromium apps have a tendency to experience memory leaks when used over long periods (and I only restart my Mac every 3 weeks or so) and purging RAM becomes a real necessity if I’m not going to quit and restart apps.
I close Chrome frequently because I hate it, so that must help. I think it is the worst memory and power hog on my Mac (and I use FCP, Xcode, Studio One a lot; Graphic is bad here too) and it makes me sad to think just browsing the web is so unnecessarily bad for the environment.
Unfortunately, Google Sheets is my favourite app.
Ha. I actually live inside four different writing apps.
I find that Chromium apps - Brave, Epic, Vivaldi, etc - are simply faster than Safari and handle most web pages better; for some reason Safari tends to bog down when visiting some websites. But Chromium apps can use any of Chrome’s extensions, and I use a ton of those, ranging from privacy enhancers to ad-blockers, to extensions that customize Reddit and YouTube, to ones that save webpages as epubs, or implement dark mode on pages with a click, or enable right-click on sites that try turning it off, or grabbing RSS feeds, or block tracking pixels in email. Firefox is a quite good browser too but has far fewer useful extensions.
And the built-in ad-blocking in both Mac and iOS versions of Brave (using, from what I understand, the guts of uBlock Origin) is very convenient, especially on iPhone.
Big Sur is supposed to make it easy to translate Chrome extensions for use in Safari, so it will be very interesting to see how things shake out next year.
Out of curiosity, is there anywhere you’ve shared the list of your favorite Chrome extensions? It sounds like you’re more into that ecosystem than most.
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Here’s a portion I listed in another thread:
Here’s just a list of privacy-related extensions:
And I mention another couple here:
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By the way, if anyone is looking for a Safari alternative, the Tab Suspender works really well.
Because of its history. CleanMyMac has broken apps in the past, including 1Password and DevonThink.
CMM looks better if it finds more things to purge, and so it tends to be overly-aggressive.
You’d have to be very careful not to have that break your apps over time.
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what would you recommend as an alternative to CleanMyMac?
I do not have SetApp but do have a one-time purchase of CleanMyMac, and think it’s worth the cost. I have used it for years and never had any issues.
I tried SetApp when it first came out and found that I didn’t use it enough to warrant the subscription. It was a good way to trial new apps, but most of the apps were useless to me, and the ones I did like were cheap to buy outright.
I’m with you on this; I can’t imagine how this would work. Flushing RAM allocated to caches would make it look as if memory is freed up, but the OS will do that on an as-needed basis by itself. Apps that leak memory can’t have it reclaimed, as the “leaked” memory belongs to the process that’s leaking it. The only way to get that back is kill the process At best you could force it to page out. I supposed you might be able to force garbage collection to occur in apps that are written in languages that use it (Objective-C does, I believe).
I’m curious to know what these programs actually do.
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Saving to disk slows down the system, virtual memory slows down the system, period. Writing to disk during pagein/pageout activity slows down the Mac when RAM gets full. Even when you have inactive memory macOS will need to do I/O first to save the data to disk before it can reuse the RAM. MacOS operations in theory meets macOS in reality, and reality wins. The Mac will slow when after it uses up RAM and has to to pageouts/pageins.
Doing a purge forces macOS to clean its RAM cache, doing I/O writes if necessary, then put the pages on the free list. Freeing up RAM is great for starting a new app that needs lots of memory and the app or data it needs has not been accessed recently. And you just consolidated a lot of deferred writes in one disk wake up. The downside is that you of course need to re-load old webpages, which is no biggie for me when the alternative is a slower system.