Its only to much when you flow is restricted to the point that your liverock doesnt get enought & constant water flow thereby the bacterial process is hampered
So to much live rock is as much a problem as to little
Exactly. And usually the point at which flowrate arond the rock is impeded is when it becomes "difficult" to aquascape it all. I realize that's somewhat of a blanket statement but usually sufficient for a beginner who won't know the nuances of flow around rocks without experience anyways.