I thought that this was a horrible idea til I tried it. Instead of $20NL I gave a try to $50NL with the profits from earlier today. I found the following:

1. It tightened up my hand selection, which I need to work on. I also played position better than usual.
2. It stopped my over-tendancy to slowplay.
3. Conversely, I didn't get the max out of my opponents on a couple of occasions as I overplayed my hands to prevent being outdrawn.

Overall, a good 1-off exercise to improve my game. I now need to move down to my bankrolled level to implement the leaks which I discovered through this. I think if you don't mind dropping the whole buy-in then once in a while this could help your game...with the emphasis on being willing to LOSE THE BUY-IN!

A nice $25 profit in the last hour from it helped my experience too