I own 5 nos of flashes (3 nos speedlight and 2 nos 3rd third party)
Most of time i bring along 2 speedlight for my macro, i had bring along up to 4 flashes to field, but i might not use them.
For me, how many external light was use mainly depend on the natural light condition and the effect i desired. Sometime i use only natural light. Of course, with more flash, you can have more control, but it is also useless if a person don't know how to tame it.