I can only explain in lay terms… I have a new MacBookAir w 495 GB however with 8 GB RAM. Half of the hard disk space is full. No regrets there. I do wish I had bought the 16 GB though as I get notifications from Clean My Mac that I’m running low on memory. That only happens 2 or 3 x per week and I just need to close out Apple Music or something; just to be more cognizant on the number of open programs. I’ve yet to get a more serious notification. It has never crashed.
Other than that it is superbly fast! Absolutely amazingly rapid downloads eg. Nothing drags!
I haven’t had a Mac in a decade so I cannot truly evaluate it. But it certainly seems awe-inspiringly splendid.