Zoidberg: Question is: do you really need to categorize ALL of your games?
I'd argue that it's more important to categorize them all the larger the library gets, so yes. Depressurizer does the heavy lifting for me and helps me discover my own games easier. I haven't played the vast majority of them, especially since many came in bundles. I love going through my library and finding a hidden gem that I end up loving. I can't do that if they aren't categorized properly. Since that's an impractical task to do manually, being able to import the work Depressurizer has already done for me is huge.
Examples of some of the categories this tool helps me fill out automatically:
Co-Op, Local-Co-Op, Local Multi-player (this sounds redundant, but isn't and has come in handy), Multiplayer, Single player, HLTB (how long to beat) 0-5 hrs, 5-10 hrs, 10-20 hrs, 20-50 hrs, 50+ hrs, Steam review score (I split it between Overwhelmingly positive, very positive, positive, mostly positive, and mixed with my own small tweaks to how those are determined.
Manually applied categories include on-deck (looking to play soon), and my personal 1-5 star ratings (which I'm glad GOG 2.0 will natively support, shame on you Steam :P).
So yea, the larger the library the more important it becomes to retain this valuable data.