Side by side view, eg. terminal + code editor. Or when I want two finder windows in sort of a total commander fashion, so I can copy/move hundreds of files around and visually inspect the results so I don't accidentally lose anything.

I always just size the windows as needed. Snapping for me is just this annoying non-feature that attempts to be more clever than me and interferes with my flow.

I don't use native snapping, just Rectangle, mostly through shortcuts (ctr+alt+left/right, and then ctrl+alt+backspace to reset window), because it's quicker than manually resizing for me.

Depends on screen size I supposed. And it is really useful when you want to open multi document/web page at same time.