"irrelevant" is badly chosen. I mean it is unavoidable to always have to send work updates, whereas tickets posted by the miner can be avoided by choosing a high difficulty.
I'm no pool operator (obviously), but keeping connections up will use up some memory and every client connected increases the latency. As I don't know the specifics I won't go into that, like I said, maybe CK can answer that.
I'll practice with the 'quote' button more so I'll only post a single replies to a topic instead of a reply to every post I quoted.