Bid strategies are cost control tools.
By setting bid strategies you are telling Facebook how much you are willing to pay for your ad to be shown over a competitor’s or anyone else trying to reach the same audience.
Facebook operates “pacing” which is raising or lowering your bid on an auction-by-auction basis. If your ad set isn't performing well or you are choosing accelerated delivery, Facebook will not pace your bid.
Facebook recommends:
The lowest cost bid strategy is used if you want to get the most value from your budget.
The target cost bid strategy if you care more about having a stable average cost per optimization event.
You can also set your bid strategy using the Hunch platform.