I find undo a real help when I'm typing fast, editing and trying different things. Often I make simple mistakes and move on or retype an error. Hitting undo is such a fast way to go back.
There are a number of keys that "undo" your last "do". I use Ctrl-/.
Its fast, easily accessible and so convenient.
A feature of undo you may not know about is "undoing" your "undo".
If you keep pressing Ctrl-/ it will get to the end of your present undo cycle and start to cycle back to your very first action. This is great. You can test different text or code see how it looks and if you feel it sucks, just cycle through undo till it recalls its original state.
A key combo I use with undo is Ctrl-g, the keyboard quit command. If you cycle through undo and find its cycling back too far, hit Ctrl-g, then hit Ctrl-/. Undo will start to cycle forward. If you hit Ctrl-g, then hit Ctrl-/ again, undo will stop and cycle in the opposite direction.
Mess around with it, and see for yourself how powerful it is. Its a great tool.