I'm intrigued by this comment just because I was originally the same way about stage manager on the iMac, on which I would always insist on using apps in full screen, which, granted, is a great experience on the big screen, but on things like Word or Teams is a bit of a waste of space. I tried using stage manager once but it made it lose memory pretty quickly, and I hadn't figured out that different views weren't limited to windows of each different app, and you could just move windows from one view to another.
Once I'd figured it out, I found that it worked great. The memory issue appeared to be just a one-time thing, and it was a great way of multitasking. I'm kind of in the same mind about wasted space, and I find the whole asymmetry of the windows a bit unsatisfying, but the big advantage of it is that you can have about ten windows open at once, and if you lay them out very strategically, it's very easy to just switch between them by just having a small side or corner of each window visible at all times. I've had big work tasks which that kind of approach has been extremely useful for.
I'm curious to see what stage manager will be like on a 13-inch iPad. I don't imagine it will be as good for productivity purposes considering the screen is a third of the size, but the big advantages of the iPad are optimising the apps for size (e.g. using iPhone layouts for smaller windows) and being able to have full-screen windows as their own views.