Quote from Writr
It measures the amount of CPU you are using, which is far from useless.
However, the fact of the matter is that f3 is not essential. The compass does a good job of helping players find their way back to where they were, and it's easy to use markers to measure distances with torches and such.
Personally, I would rather Notch work on getting Minecraft to run better performance-wise rather than make that toggle-able (especially since it isn't technically a player feature). If he switches from using Java to something more CPU-efficient, you wouldn't be having this problem in the first place.
It is obvious that you work very close to the spawn, and do not spread out projects along a large world to create a regional effect. For you, the compass would in fact come handy. Of course, for someone X12000 and Y-16000, having objects a few thousand meters apart can be a bit of a problem when relying on a compass.
Also, say you don't primarily travel above ground, like you obviously do, placing markers and bothering yourself with landmark memory when there's a perfectly good co-ordinates system(nearly perfect, there tends to be this read blob that covers it on slower computers). You pop up after spelunking for a couple of hours, and use the co-ordinates system to travel back to home sweet home, there's no denying you haven't done this at least once.
I'm truly sorry that you need a pretty visual graph to tell how your CPU is doing. I understand numbers are complicated and things like opening up task manager and viewing CPU usage are very time consuming and nobody can be bothered to do such a horribly boring thing. That is why, for people like you, I think that the graphic should remain as an option, so you don't have half a heart attack when you don't know exactly how spikey minecraft is making your CPU graph look.
Unrelated, Minecraft is a BROWSER game, meaning the options are pretty much Java and CS5. Since >CS5 >Minecraft is basically laughable, Java is the obvious option. Of course if you want to be a selfish ******* you can attempt to demand that minecraft becomes an application-only game, and uses a "More CPU efficient code", implying that minecraft isn't inefficient at CPU usage and java is.