Issues are essentially bugs, feature requests, or suggestions that you believe should be incorporated into the theme. Anyone (with a Google account) may file an issue and it will be tracked accordingly. It's simple.
For our purposes here, a bug is when the theme does something that it explicitly shouldn't, whether intentionally or accidentally.
Before filing an issue, however, consider:
But it's better to suggest something that isn't incorporated instead of keeping it to yourself.
And thanks for taking the time to check this out. Your input is both welcome and needed.