Looks like my question was answered in a sibling thread. The behavior of Alt+Click/drag is to allow you to click on any part of a window and move the window.

Looks like my question was answered in a sibling thread. The behavior of Alt+Click/drag is to allow you to click on any part of a window and move the window. It is extremely useful not just from time-savings (no need to click on the top bar to reposition a window), but also to be able to grab windows that are positioned off-screen or beneath another window and move it with a single operation.