He leaves tomorrow [color=darkred](“leaves” refers to the future)
He is leaving tomorrow [color=darkred](Does “is” refer to his future state i.e. tomorrow/time of his action OR is it referring to his existing state i.e. right now, at the moment of speech?)
You may also take a look at all the different tenses for comparison.
In this site, you will discover that the names of the tenses are not totally necessarily related to the actual time of an action. How to use the appropriate tenses depends upon the criteria, conditions and some rules. That’s why we can use future tense, and sometimes present tense or present continuous tense to mention future action.