I think the RSS feeds comment was me. 
(edit: oops. Hit enter too soon.)
I’m still working out the kinks. It isn’t as nice an RSS reader as most RSS apps, but it is where I keep all my other readings and reference materials. The purpose of using it for RSS was to centralize the place where I do that kind of work. The main detriment of this approach is this: using DEVONthink and DEVONthink To Go (DTTG) requires running your feeds on a Mac and syncing the feeds database with DTTG every so often.
Otherwise DT currently has two main uses for me:
- Its URL scheme is wildly powerful (Federico Viticci wrote about them here.) x-devonthink-item:// links, for example, allow you to create universal links for files and use those links on all your devices. I have used this to build in links to specific PDF pages in flash card study using Anki, for instance. I also use this to refer to specific templates and pull other kinds of data in Shortcuts.
- DEVONthink provides indexed full-text search for everything you stick in it. I have a Library database with 4,000 books, papers, and other resources that I use to keep all the materials I’ve ever used. I’m pretty good with search, so this allows me to avoid having to organize these into arbitrary folders. As a bonus, DEVONthink’s text processing includes some handy tricks—I have a rule, for instance, that automatically adds tags to a reference file based on DEVONthink’s concordance text analysis.
In short, I hate putting energy into maintenance of content—both putting files somewhere useful and then finding them later. DEVONthink takes care of a lot of those tasks for me.
That said, I think I’m using DT to about 20% of its potential for me. That doesn’t necessarily mean that it’s this amazingly powerful app—arguably it should be easier to use it to 100%—but that there are many imaginative uses that are easily overlooked. As apps go, it takes a while to understand its capabilities.