This may help or make you sorry you ever asked - [broken link removed]
Starting at the end of you question, wheel balancing is done on each corner of the car individually while tracking and alignment is done on each corner relative to its companion wheel on the same axle as well as relative to its companion wheel on the same side of the car.
Wheel balancing can be done with the wheel on or off the car and should be done each time you mount a new tyre on a wheel. The process consists of spinning the wheel and adding weights to counter-balance any vibrations that arise. These weights can be clipped or glued to the rim.
The outcomes of an accurate tracking and alignment job can be any or all of -
- adjustments to the various adjustable components of the braking or steering on the car (threaded rods, lock-bolts, etc.)
- replacement of worn rubber-bushings in the steering or suspension
- replacement of worn steering or suspension components.
While ideally all of the parameters that can move out of alignment are readily adjustable, this may nor necessarily be the case. If your local tyre-fitters say something like "The camber on the rear of your car can't be adjusted" interpret that to mean "We don't have the measurements, the jig, the training or the time to be bothered, and while the machine cost us €50k, we never paid for training on it and it has never been re-calibrated since it was installed 6 years ago and the software is equally out of date".
I have yet to identify a single outfit in the Republic of Ireland that can do an accurate steering and suspension geometry adjustment.
Excessive wear on tyres can be a result of incorrect tyre pressures as much as steering or suspension problems.