Many issues I've submitted are simply bug reports based on my observations during usage.

Simply by saying "hey you may not have noticed X but when you do Y then this happens..." it can help the author(s) know:

* that a problem might exist in the code.

* that there's no problem but the docs made something unclear which led to the problem I reported.

* how others are actually using their software.

These are worth paying for on their own.