I was referring to the varying pressure from a full tank to an almost empty. If you tune it while it's full, it's off when it's almost empty...if you tune it for performance at the end of the tank, it is off for the first half tank.
It isn't a big deal for the most part, as you can find a happy medium that covers both ends of that spectrum.
But you can convert a nitro engine to run without the pressure line, and not have to deal with that at all.
It gives the throttle a more linear feel in the lower part of the powerband...Not quite so peaky, and easier to control.