Safety is the number one priority, at least with my trainers. Anytime someone hits their head they give them a few moments to recover before they make them roll out and then get checked out. If someone is getting blown up while doing moves, they make them take a break. If you hurt something, you aren't judged for walking it off or sitting out if its a more serious one. We are always being reminded to tuck our chin to make sure we don't smack the back of the our heads. If someone is taking a bump or move wrong over and over, we simply move on and then them try again later.
Accidents will happen. I've been dropped on my head on a failed body slam. I tripped on a guy during a float over and slammed my chin into the mat while rolling out of the ring. I had a guy land full weight on my elbow during a back suplex. I skinned my forehead on a mistimed DDT. We had a girl two weeks ago who had someone land on her hip and pinch a nerve in it and shes out for a bit. So just like any physical activity there are risks, but we all do our best to minimize them.
As far as the balance goes, it isn't the moves that matter. If you work the crowd properly you can go out and excite the crowd with very simple moves. It's always about the story. While the level of athleticism in pro wrestling has never been higher, so many guys who can do those breathtaking moves can't use them in a way that makes sense. If you just bust out high spot after high spot and huge impact moves over and over, they lose their allure and on top of that the wrestlers will wear down quicker. So mostly, its simply about knowing when to to execute the riskier moves to get the biggest reaction. That said however sometimes you just have to bust out something crazy in a big match to really wow the crowd.