I believe there's a recent push from StackExchange to make it easier for New contributors to successfully join the community, and I think the Bounty functionality leaves a lot of room for improvement.
What happens when I start a bounty?
The bountied question will appear with a special indicator in all question lists, and it will also be visible on the homepage Featured tab for 7 days. Part of what you’re “paying for” with the bounty is to get additional attention for your question, over and beyond what a normal question gets. In that regard, a bounty does not guarantee a response, and reputation refunds are not available if no answers are received as a result of the bounty.
Note that it says, "visible on the homepage Featured tab for 7 days" (it specifically doesn't say "up to 7 days", it clearly and unconditionally says "for 7 days"), but that's not what happens when someone actually awards it (prematurely, before the 7 days are up), e.g., the current implementation doesn't actually fit the spec as documented.
The promise gets broken the minute you make an award of the bounty (outside of the 1-day grace period after the 7 days of the bounty being featured in the Featured tab of the homepage). This is a problem because:
New bounty contributors don't seem to realise that lots of folks look at the Featured tab, which is sorted by expiration (oldest bounties first), to see interesting and worthwhile question/answer pairs, to learn from, and to upvote.
In my experience on Stack Overflow, most of the upvotes happen in the last 12 hours of the 7 days, because it is the 6 day old bounties that would show up at the top of the first page of the Featured tab from the homepage of stackoverflow.com.
In fact, that's a pretty easy way to earn a lot of reputation, for both the asker and the answerer; all of these facts are well known by the top active users, and are vividly written between the lines in
/help/bounty, too (where rules against overpromotion are clearly documented), but it's not actually explicitly documented there at this time for the newer contributors, nor is it something that would come natural if you're a New contributor.
For experienced bounty contributors, there's an anti-pattern on the other end, where they have to wait until the very last minute to award the bounty (e.g., during the 1-day grace period), which is short enough that it's easy enough to miss it entirely, and then at least half the bounty may go to waste.
I would imagine that some users may have gotten burned with awarding the bounties prematurely in the past, and may resist any sort of action, trying to get the most out of their bounty, which may possibly involve losing half of it due to inaction. (The correct pattern would be to do an Accept Answer as soon as a good answer is available, and changing it if a better answer does come along; but it's also easy to see how having being burned on the bounties in the past, might prevent you from trusting that an Accept Answer is always to your advantage here.)
The current best workaround for both new and experienced contributors alike is to use the "Accept Answer" functionality to trigger guaranteed eventual bounty award in full to the accepted answer.
This way, one can accept the answer at any time, change their mind at any time, the full amount of bounty will always be awarded to the accepted answer after the expiration of the grace period (unless manually awarded at any other point) and the question will continue to remain on the Featured tab for the whole 7-day duration, including at the very top of the Featured tab in the final minutes of the bounty, where both the asker and answerer have the potential to receive a significant number of upvotes (which are most likely to come in the final 12 hours of the 7-day period when the bounty question bubbles up to the top of the Featured list).
This is a preferred approach even for experienced contributors, because it has no downsides at all. In fact, it shows everyone that the answer does solve the problem, hence, it's much more likely for both the asker and answerer to both receive a whole bunch of free upvotes for providing obvious value to the community — compared to an abandoned question, where it's not exactly clear what's going on, so, passer-bys are less likely to upvote the question and/or answer if they have no clue what's going on, or whether all the dots were connected and addressed.
I think the proper long-term solution would be for StackExchange to implement one or more of the following changes:
Fix the bug where a premature award makes the question disappear from the Featured tab (this part is a bug that conflicts with documentation).
In fact, if the answer was so good as to warrant an immediate bounty award, then more people should see it, not less. Making it disappear from Featured is a disservice to the community, where the whole point of the site is supposed to be to learn and see success.
Make it possible to unaward the bounty at any time during the promised 7 days. It is clearly documented that bounty awards are final (so, this part is up to the spec). Personally, I think this part is more of a workaround against the bigger issue, e.g., the prior point where a premature award hides the question and answer from getting more attention. (Awarding a bounty by mistake to a wrong answer would be a separate issue.)
As a variation of the above, make the bounty award button behave the same way as the accept-answer functionality, where it can be changed at any time (within the 8 days), and doesn't make the question disappear from the Featured tab. This is probably the ultimate solution, as it may simplify the paths and reduce the documentation overhead/burden, plus would also work in situations where the bounty is offered not by the asker of the question, but by a separate contributor.
I believe this is a "bug", as the feature as implemented is not in line with the specs as documented.