After teaching my "60 AutoCAD Tips in 60 Minutes" class at Autodesk University - a friendly attendee reminded me of the popular OOPS command (sorry I didn't catch his name!). The OOPS command was AutoCAD's early attempt at an Undo command - and was a lifesaver (or job saver) in many cases. 30 years later - the OOPS command is still a handy tool to keep in your AutoCAD tool belt.
The OOPS command brings back the last item(s) you erased...plain and simple. It doesn't matter how many operations you have performed in the meantime - it is happy to bring those deleted entities back from the dead. Of course the Undo command will do the same thing - but it will also undo all the actions taken since you performed the Erase - and that might not be so desirable.
Check out my Cadalyst video for more info:
Bonus Tip: Watch the video and learn about adding markers to your drawing for the Undo command!