Checkpoints allow for partial level rewind so beginning parts of levels don't need to be played over and over to get to difficult parts.

Early on you are limited in placement, but in later levels you can and need to build your own mazes to really direct the enemies. There are lots of options/routes/ways to build those mazes so it really opens up a lot of replayability to try and beat your friends scores by tweaking your mazes for maximum points.