As some point in time you would want to re-use an ESXi host but do not want to go through the hassle of a complete reinstall and rather have quick solution.
I find the "reset system configuration" in DCUI very useful for this task.
There is also a way to perform this task via SSH:
# /sbin/firmwareConfig.sh --reset (this will automatically reboot your host)
# /sbin/firmwareConfig.sh --reset-only (this will not reboot host and needs to be done manually)