I have every single app on my phone all organized into folders on the first page. Being able to "banish" the apps I use once a year to the app library to clear up space for essential apps+widgets is a dream to me.
Looking at my phone right now, I'll have 12 frequently used apps at the bottom (last two rows and dock) and the top 4x4 filled with widget stacks. I'll use the widgets for glanceable stuff and as a launcher (ie Fantastical, Things, Notes, etc). And then if I need anything not in my widget stacks or the bottom apps I have search.
I don't even personally care about the App Library as a browsable thing, I care about it as a "get 150 of these apps off my home screen" thing.
its a little odd to me still. They don't 'disappear' - they're still in the last page, but now its an automatic list. I kind of had that anyway - a 'dustbin' page with a few folders crammed full of stuff I either never used - like preloaded apps, or only used via search. So I'm still finding it slightly confusing the actual benefit.