When during sex i fullfilled my partners desires and ended the session it showed that how much desires I fullfilled but what are those ''points'' do, because its quite highlighted just like when I would gain a 'Essence' from the session.

If my memory serves fulling desires increases lewdness by a few points. A little message should appear in the "dialogue" window on the turn that the desire is fulled saying that lewdness was increased, though i don't remember it saying by how much. You can check by mind reading the slave before and after a session to see what the difference is.