I know you shouldn't, but I bind while working out. Worst case scenario, I feel sick and have to stop (which, even without a binder, happens to me a lot anyway). Best case, the binder helps me sweat more from my chest. I have a binder one size too big, so it's not as dangerous. Unfortunately, since it's a half binder and it's a little big (by binder standards), the bottom sticks out under my chest, which is visible under my grey gym shirt. :/
I used to wear a sports bra with a neoprene belt under it sometimes (my shoulders are too big to fit sports bras that would conceal anything), but the binder works much better. It hinders me about as much as wearing a sports bra by itself, so I'd rather look and feel more comfortable.
Once I get top surgery, I'll have a whole new world opened up to me in the way of working out. I often can't breathe if I do cardio first and then try to do an exercise where I need to raise my arms above my head. So once I lose the binder, I'm hoping I can push myself much harder and workout however I want. But I also have a lot of health problems, and no matter how fit I am, I get winded going up 2 flights of stairs. So who knows, I might not really see too much improvement in my workouts without a binder.