[Al Skierkiewicz]

Something that helps software out is knowing where certain parts of your robot are. Pots (variale resistors) connected to moving arms, steering mechanisms, etc. can report back to software and help modify robot reactions and assist in auto modes.
Microswitches can be used to limit travel or sense when a moving part has just about reached it's mechanical limit.
Wheel encoders/shaft encoders can be used to tell how far you have driven.