yeah, lunar cycles play an important part in many cycles in the ocean, but if you dont have them then it realy wont make a difference in your tank.
and yes, they do help sps corals spawn, that and temperature spikes together. a few days after a full moon in july (that is usualy when the temp is right) they will spawn. however, none have ever been raised in captivity or even fertalized. it will jsut mess up your levels by a LOT.
so it is mainly for looks