Throwing off mound or flat ground between starts


I have a dilemma, my sons pitching coach insists on having him throw flat ground bullpens in between his appearances. I personally feel that throwing off a mound for bullpens is better. I’m sure this is personal preference but I’m curious as to what others feel is better approach??


I only play catch and/or some 120-150 foot hard throwing from flat ground.
Pitching is done from a mound. I only practice pitching from a mound. If you aren’t on a mound, in my opinion, you are just playing catch.