For myself, my horse had a rearing problem before I taught it to him. He was dangerous, throwing himself up into the air, grabbing the bit and fighting. After he threw himself over backwards, almost landing on me, I had two options. First was retire him permanently or the other was try to teach him to balance himself. (All other options had been tried and failed to get him to stop rearing)
So I taught him to rear by collecting his weight onto his hindquarters and holding it. I taught him to not explode off his hindquarters or throw himself anywhere. He learned to keep his hind legs underneath him and keep his balance.
He has not flipped on me since, neither has he come close. After I taught it to him, it was something that I made him do and it was under my control...so he stopped using it as an evasion technique.