I've been wondering this as well for a while now. Seeing your post i decided to investigate.
After digging through these forums for a while i found the answer. (big thank you to Warr for pointing it out)
http://www.roempire.com/database/?page=misc&act=weaponsizetableThat shows what % damage all the different weapons do to different size monsters. In your case (and mine) using the DBSS mace in nif, which consists of monsters of all different sizes, weapon perfection would help. The mace already does 100% damage to medium and large monsters; However it only does 75% damage to small monsters (Heirozoists and Quves/Ludes). so by using weapon perfection, you'd hit those two for 100% as well.
Although using it is completely up to you, if you have SP to spare, go for it. But if you use "Maximize Power" and SP is a problem, you don't have to use the skill and save yourself some SP/GJ.
(and for any axe users out there reading this, Weapon perfect is almost a must since axes only hits Large monsters (gibbet only) for 100%)