Distance is the factor. APS-C and FF cameras also require different lenses. When I photograph events, I have tried my 7D with primes, and have to crank up ISO so high that noise is a problem, so I use FF. I take along my 35mmL, 50mm f/1.5, 85mm f/1.8 and 135mm f/2.
Then I use the one that fits the distance to the performers, and I can put on the 35mm if I need a wide view. I find f/2.8 lenses to be too slow most of the time, because i am using 1/320 sec shutter speeds wherever possible due to motion.
Distance, motion, lighting all these can vary, so there is no way to know what you will run into.