If you are shooting a BIG show that is very well done, they will be flooding the catwalk with light and you can shoot as the gentleman mentioned. If you are shooting a local show, it is VERY rare that there is good light where you can shoot at high speed at f2.8. I always take lighting equipment with me so if I see a need for lights, I have them. I agree that shooting with ambient light is the BEST but reality for local shows in my area is that you can't because the light is crap. Be very aware that the light for the actual show is OFTEN much less than when you are setting up to shoot an hour before the start. If the light in the setting comes from diretly overhead and goes directly down, you will get some serious shadowing with available light. Flash fill will help GREATLY!