Undo is one of the greatest things a computer can do for you, and here’s a timesaver for blender’s undo:
If you’re adjusting some number, and blender takes a while to compute when you change it, then you know an Undo will also take some time. Sometimes, when you Undo, you notice a delay even for stuff that doesn’t take blender a long time.
Avoid some of that delay with this Undo habit.
To save time, look first at the Undo History. Ctrl-Alt-z (Cmd-alt-z on a Mac) pops up a menu of recent changes. Often, a numerical change will be shown with the value that you changed! That means you can glance at the numbers before you undo. You can even hit Esc and type the number you saw instead of using Undo. It’s usually quicker, in my experience.