I am an Alignment Ace
My rule of thumb you are only asking for trouble when installing tires and not checking the alignment.
I concur HUNTER led-sensored machines are great.
Type in the make of the model, it spits out suspension geometries, even better it shows digital captures of where the vehicles caster/etc adjusters are.
This is very useful on vehicles (esp, european, caddilac etc) with there complicated Independent Rear Suspension set-ups.
It also produces a before and after printout.