1) It decreases load on the server by not asking for work as often, which benefits the server.
Seems like it would be better for the entire community, if you simply worked with other pool servers to accomplish the same goal.
If you support long polling, then the default upstream poclbm (m0mchil's) -- and soon, every other miner -- will only ask for work once every ~60 seconds.
Community standards like this benefit everyone.