In my opinion the only time when Stoneskin is a must as a pre-buff is in a boss fight where damage to someone who is not the tank is pretty much guaranteed to happen. In fights like that I like to put Stoneskin up before the fight to give me a little breathing room. It typically frees me up to do something besides spamming Cure/Cure 2 trying to heal the dps with spot heals earlier in the fight. Also if the tank is going to whine just give him what he wants. There have been plenty of times that I have LONGED for a tank to slow down so I can pre-buff on a fight I thought needed it but they wouldn't. If you are getting asked to pre-buff just let them have it at least they recognize that it is useful even if they are being a little obsessive.