I am assuming you are referring to betamethasone valerate, which is essentially a type of cortisone, which is an anti-inflammatory hormone.
Dr. Lee used to use it in his formulations several years ago to help reduce the irritation and inflammation from topical applications of medications. He has since (as far as I am aware) stopped adding it to his formulas, but you can request it from him and he may still include it.
My take on it is that it is not necessary. You want to avoid repetitive use of cortisone due to potential harmful side-effects when used over the long-term.
It doesn't do anything for hair loss, it just may help reduce irritation from the topicals.