Is coral covered live rock still a viable filtration media, or a nutrient trap ?

[gregzz4]

I see many beautiful tanks overrun with enviable corals and want to emulate them. But it makes me wonder about the lr being 'plugged up' as it's covered.

My better half wants me to over populate our rock, and I agree it looks great, but hows it for phosphates and such that may/are trapped in the rock ?
Wouldn't this lead to 'old tank syndrome' ?

Thanks for all input
Let the debate begin ...