Well, the mastery skills effects are stated where you can choose them...
As far as I know, we now have the following masteries (not sure for all clans, since I only glanced at them apart from my BoT healer):
weapon mastery - damage bonus (the "old" one)
clan's primary weaponweapon mastery - critical chance bonus (after maxing that weapon's damage bonus)
clan's primary weaponweapon mastery - damage bonus (the "old" one)
clan's secondary weaponweapon mastery - critical chance bonus (after maxing that weapon's damage bonus)
clan's secondary weaponweapon mastery - damage bonus (the "old" one)
bracersweapon mastery - balance bonus (after maxing damage bonus)
bracers"defense" mastery - adds to defense vs. one attribute, e.g. Yang (whatever these attributes are/do - but since demons got a Yin/Yang damage buff...)
available after maxing the two masteries for one weapon"passive" mastery - adds a bonus to something, for BoTs to anger growth, i.e. rage more often
available after maxing "defense" masterymastery skill - gain a new skill (...), e.g. berserk rage for BoTs (damage bonus, huge defense penalty, defense becomes NEGATIVE!!! - kill fast or be killed even faster!)
available after maxing "passive" masteryIt's not yet clear whether all the masteries are actually worth the points, but a damage or critical bonus is always welcome, additional defenses might come in handy and "passive" mastery and mastery skill can be useful on occasion (depending on clan and thus their effects).
Additionally, if you max your role's weapon masteries and the "neutral" ones (those not depending on a weapon), you'll still have loads of points to spare. So if you want to get all available masteries...
If you have put points into weapons not associated with your clan (e.g. spade mastery for demons), they seem to be lost at the moment, but the mastery reset after attaining your second role (or whenever you can reset masteries) might return ALL the points. Not sure about this, though.
P.S.: Yes, MurongXian, as far as I Know, hardness is supposed to work as a kind of "refinement insurance".