Anybody here tried using 2 flashes, specially during the reception?
I've seen a photographer used 2 flashes before. One flash was on his camera and the other one was on a monopod held by his assistant. Does anybody here knows the proper set up for that? If the on camera flash is +2/3, would you set the off camera flash to +1...etc?
Thank you in advance.

It really depends on the distance between the flash and the subject as well as the desired lighting effect. I have used two flashes and often dial down or turn off the on camera flash to create a very dramatic rim lighting effect. I am not familiar with the canon system however. Good luck.