Exactly what it says on the tin. If you have coins/bonus stars, those get converted into star power time at the beginning of the next level. You can increase the star power time by commenting in more ASLs in that section (Every ASL multiplies the star power time by 2).
Sadly, I have to reject this because of one thing, and one thing only: when I apply the 'coin gives you star power' code, it won't reset the coin counter upon level start as it is intended. Maybe you could use, in this case, $0DBF directly, in order to reduce code and make it work. Otherwise, the other code is fine, so just fix this issue and this is ready for approval.