When a coral grows too big?

[msjboy]

I saw a guy with a silmilar sized green monti..maybe even bigger under my lights…nothing else in tank as he was getting rid of it. Not sure what happened to,it but he was going away all the pieces that had broken off. If I recall, it was even denser in the number of petals. Tank was a big plexiglass one probably at least 150 gallons.