When you need to use direct on-camera-flash in a very dim lighted place and need to use very high ISO and max aperture, like at a reception or a wedding dinner. Then the lowest settings isn't low enough.
Canon has solved this problem with their flasgship flash EL-1.
It is very annoying when I take my A1s for short citybreak that I have to take big charger as well. USB-C plug inside the battery would be perfect idea!
