How important is light acclimation?

I've been reading a lot about light acclimation and I'm wondering how important it is. Any negative experiences with no light acclimation?



Is it more important when going to LED from another type? My LFS uses LEDs for their frags and I have them on my tank as well.



If it is important, what time frame should be used? I read one source that said you should slowly move the coral over a month but that seems excessive.