Earlier quoted context omitted.
To add to this I remember when OS X came out there was a lot of groaning about how slow window resizing was. Years of improvement later it still lags a hair. Noticeably slower than windows.
I think one of the reasons is that OS X provides automatic double-buffering of window content at the OS level (it also has a somewhat different drawing model than Windows), which adds a bit of latency but reduces flicker. Another factor is that Mac apps typically adapt themselves to the size of a window, and resizing will trigger a redraw of everything . Apps like Mail have always been really slow at redrawing themse…
Oh, and OS X actually resizes windows at a fixed frame rate. You can change the rate with:
defaults write NSGlobalDomain NSWindowResizeTime -float 0.001