So far, I can talk only about phals...I always leave them alone until they're dead. Although it never happened to me, that's where new keikis are born.
I've found a good example at home. This phal is a keiki I took form a spike, 6 months later it bloomed and I never cut the spike since it was not dead. Now, something is growing from it, I don't know if it's a spike or a keiki.