What's the difference between a trans male and a cis male?

*A trans male was born female* - popular answer

What does that matter if they are now, with their entire being, a male?

Why is there a need to add further labelling to a sublet of people who are the same?

By adding the presets 'trans' and 'cis' are you not just dividing a group of people as to ensure that they will never be considered equal?