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.
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.