encrusting- affect live rock?

Just curious if there is any sort of impact with coraline growing over live rocks, or if there were a lot of encrusting corals in a tank that covered a large amount of rock, would the biological filtration of the live rock be reduced by any significant amount. Since there are a lot of tanks out there successfully running with tons of coraline and encrusting corals and algae etc. it obvously isn't detrimental but I was just curious- one of those things I just start thinking about lol ;D, it seems like it would cover a lot of those nooks and crannies where good bacteria could populate.

 

There are many area that will not get encrusted so the effects are small.