In what situation would using FEB (Flash Exposure Bracketing) be a good idea? Exposure bracketing can be blended together with HDR, but why would I use FEB?
You seem to have lost track of the original reason for AEB: To be sure you nailed the exposure. In this case you use small increments (up to 1 EV at most) while for HDR you would use larger steps (at least 3 stops but 5 is good with modern cameras).
For FEB, it is the same: To be sure you nailed the flash exposure.