You won't respawn at the checkpoint if you have <25 coins. Each time you respawn at checkpoint you lose either 10% or 25 coins, whichever is higher. I know this from the code. Players do not know this. It should be explained, and we need to discuss if it should be changed.
The 10% or 25 coins thing is explained in the first level since https://github.com/SuperTux/data/commit/aaad57f96eeb8b3d053f4c830fb68ac9642839d4
The reason I made this issue is because we are a mario clone, not a sonic clone, and I cannot work this out in my head.
Why not just do a number of lives, as this is what most people are used to?
This behaviour is good when levels of an author contain loads of coins, so Tux doesn't get loads of lives. It's exponential, so he becomes only a few lives extra.
It has been decided again the concept of lives as well as removing the link between coins and checkpoint respawning. See #1410