People generally have pretty good spatial sensibilities, and I feel like modern OS designers seem to forget this. You feel this especially on iPadOS.
Physically arranging windows allows for a much more solid multi-tasking experience, and encouraged direct manipulation of content e.g. drag and drop. Transient "palette" or "panel" windows allow for a short term buffer (think a find/replace panel). To me, this is what made macOS so great for creative tasks. It activated my spatial memory.
I'm grumpy about the recent trend towards apps living in one monolithic window. Apple's going down this route with their recent app redesigns from multi-window to single window, likely due to a (selfish) desire to unify with iPadOS. Electron adds a dev tax for multiple windows, such that folks don't really think to do it.
I think this trend is probably due to the convergence of desktop app design with the web, which is inherently single window -- and traces its roots back to window.open() being abused by pop-up ads.
It's unfortunate because a single window user experience is limiting -- and people are forgetting that anything else is even possible. I miss the days when chat apps had separate windows for each chat, and a buddy list you could pin to the side of the screen.
(If you've only ever got comfortable with a windows-style "maximised window" approach, you'll probably disagree with me, however).