Well, let's see. You could be singing your heart out in a production and you pause a little bit too long on that last note of your solo and you get hit from behind by a moving line of prancing choristers who were staying with the beat. Even if you weren't.
Musicals are hard on you physically. Performers truly, really sing and dance—and act—their way through hours-long productions. Five, six, seven, sometimes eight days a week. Major and minor players croon and prance and emote, and not in slow motion.
So you gotta keep in shape and on your toes. No matter how careful and judicious you are, on a stage set with actors, something is bound to happen. You could have your back to the audience and as you retreat into your role, you may notice that you're about to fall off the stage into the orchestra pit. Or you may be one of those actors twirling around in an aerial stunt in a knockoff of Spider-Man: Turn off the Dark, and take a 30-foot plunge (non-fatal, we hope). Or, or, or...the possibilities of physical mishaps are endless.
Be safe, not sorry. Keep that insurance policy current. And eat that apple a day.