Responding to the original post: it makes perfect sense to me. Suppose you are the captain of a loyal band of 40 Mounted Sergeants. You're feeling good in the company of 1400 of your brothers-in-arms. Then you get the order: Go run over where all those enemy troops are, and get them to attack you, then run back here. How would you feel?

As a side note, I think Horse Archers are best for this purpose. Very useful when they can attack a group of melee units with their backs to your main force. When the enemy melee attacks, they'll naturally skirmish back toward friendly forces, keeping out of melee range. The best bet I've found is to have two different units for this function, with one recovering their nerve while the next one draws the enemy, then switch off for the next run... their morale seems to last longer that way.