Damage, no, no damage, but slowdown, yes, of course, every cpu will be working on a frame, so of course, it will be cpu intensive, depending on your render settings. But rendercows work in the background, they are in low priority ( well, this is Windows, I don't know about macs) in the task manager. The computer running the network rendering manager ( called Hypervue manager) will not be available for other tasks, and it has to be the most powerful machine in the network. managing the cows ( cows are rendering nodes),  is the most cpu intensive task.