Chalenge, it is perfectly legitimate if you want to know how much performance room you have left as you tweak settings for the game.
If you tweak the settings offline and end up at 70FPS, there is a really good chance your performance will drop like a rock when you get online in some action. Whereas, if you tweak the settings and the performance drops to 140FPS offline, there is a good chance the game will be pretty smooth once you get online and into some action.
If you tried testing with vsync on, you would not know about the overhead you have available.
In other words, it really only means something in the context of your computer. It is not something that useful to compare to other computers.