I don't seem to understand how I should use `start`/`end` parameters to [`str.startswith()`](https://docs.python.org/3/library/stdtypes.html#str.startswith) and [`str.endswith()`](https://docs.python.org/3/library/stdtypes.html#str.endswith). Is there a simple rule I can follow?

Also, is there any benefit to using these functions compared to using string slices?