For example, the keyboard shortcuts for snapping a window left or right let you customize how wide the window is after the snap. So for example, alt + ] snaps the window to the right half of the screen. The same shortcut again grows the window to 90% wide, then 80%, then 60%, and finally back to 50%. So if I want whatever I'm reading to be decently wide at the cost of letting my SSH window take up slightly less than half the screen, I can make that happen without a mouse. Or for a good responsive site, 20% or 30% of my screen is all the site needs.
In addition, when I have two windows each taking up 50%, hovering on the window edges they share them brings up an additional handle that lets me adjust the width of both windows simultaneously (if I want). Why can't Windows do that?
Finally, there's a keyboard shortcut for centering a window on the screen, which I am a total sucker for.