In reply to: "Mignon Fogarty @grammargirl@zirk.us: I have a Mac, and when I try to drag my windows around on the desktop, they often snap to expand to fill the whole screen, which isn't what a want."
Via @dmoren@zeppelin.flights on Mastodon:

@grammargirl You want Settings > Desktop & Dock and scroll down to Window Tiling. Turn off "Drag windows to screen edges to tile" and “Drag windows to menu bar to fill screen." It's a relatively new feature, but one that's way too easy to trigger accidentally!