Bill,

If you are doing 3D maneuvers or large vertical maneuvers or climbs, the plane will want to pull left. This is particularly true with the long, low pitch props and with the large engines. In a harrier or hover, for example, if you don't have right thrust, you are constantly holding right rudder while working the other 3 controls. A little right turust makes everything a lot easier.

As for mixing, the situations are too varied. In knife edge, you can easily mix out unwanted roll and pitch, but the rudder required varies with the maneuver.

There is nothing sacred about mounting at 0-0, and most sport planes do very well with this set-up. It is just makes flying easier on many specialized type planes to have a little right thrust.