Does No checkpoints mean no respawning a checkpoints or no changing characters at checkpoints?

I'll take that you are talking about the IL categories. No checkpoints basically implies all runs must be done under a single segment. So using checkpoint under any circumstances e.g. dying is not allowed, even if you retry from the last checkpoint using the same character. That being said, changing characters mid level is of course, not allowed.

Thank you.

Why does it matter if you die though?

Because if someone did a good run and then died he will return and play until he does that segment perfectly like a segmented run that's why It's not allowed to complete the run after dying.

Okay that makes sence.

wait does that no dying rule apply also to the any% category?

oh that's a relief, i died a lot in my speedrun. also switching characters mid level is allowed too?