It's a diagnostic tool. If you know approximately the average and top end of the spectrum of DPS, it allows you to more accurately aim for it if that's what you're looking for and to see where others stand in relation to their job's averages and top ends. You don't need it, but it certainly helps if you want precision. Just like in any other game, not every one will run one and not everyone will care. Those of us that use it use it for the purpose of refining our rotations and priorities. In group play, we can see where and who needs to tighten it up. I won't expect it from PuGs, but only with like minded players, which is what statics are for.