I've read over the general guidelines about bounties, and they mostly seem to be about drawing attention to a question and getting users motivated to write better answers.
But what if a user has already offered a good answer that obviously required a significant amount of research or effort? Can it be appropriate to offer a bounty, knowing that you will likely award it to an existing answer?
Obviously, if the bounty causes someone to offer an even better answer, I'd award it to the new (better) answer. But I've seen occasional situations where users sometimes offer bounties obviously aimed at rewarding existing answers. Is this encouraged/discouraged?
The obvious benefit (from my perspective) is that a bounty rewards better quality answers and encourages users to write them, regardless of whether it is offered before or after the answer is written. However, I just want to know if there are guidelines/constraints on such a practice.