As for me it is not preferable to sell bounty token at loss even if we don't spend money of buying fot it because in the first place we spend much time of complying all bounty rules and I believe that time is money if we wisely use it, so selling at loss is not worth it.
given that you dont buy the tokens which simply means you wont loose anything even if you sold all the tokens that you got from a bounty but you still have a point . money is time an we spend so much time in doing the bounty works . although if you really need the cash , let say for important use because your loved one is in the hospital or you will be celebrating your birthday but you dont have enough cash for spendings . this was a reasonable moment to sell your coins .