Here's a pretty good blurb about alignment from Bridgestone:
https://www.bridgestonetire.com/tread-and-trend/drivers-ed/tire-alignment
Basically, when driving on a flat level road, if the car wants to pull to one side, you need it aligned. If the tires are wearing unevenly...one side more than the other, or the fronts much faster than the rears, you need it. If the tread is wearing so part of the tread block wears faster than another part of the tread block, yep. Vibration is a different problem. Vibration is from tires that are out of balance, or out of round, or have road force problems where part of the tire is softer or stiffer than other parts.
On the basis that the customer is (sometimes) right, have them write on the repair order that the new settings must be in the middle of the allowable range. Some cars have the acceptable spec so broad that the car can have one side at the bottom of the OK range, the other side at the top of the range, it's "in spec," and it's a horrible job. Demand that you get before and after print outs that show the settings and the specification. Do not accept a job that is not at the center of the specs.
Some cars do not allow all the adjustments to be made--caster is one that is often not adjustable, and sometimes camber. Some have rear toe adjustments, and some don't. If anyone knows the specs for our cars, please post them.
Toe-in is the amount the fronts of the tires point inward toward the center. The spec'ed amount is just right. This is for fronts and sometimes rears.
Camber is the amount the tires either tilt inward or outward. A slight inward tilt at the top may be good, if that's adjustable.
Caster is the slope of the steering axis. If adjustable, I like it set to the max of the allowable range. It often is not adjustable on many models.
Do not let them set the alignment to compensate for road camber; the slope of the road surface away from the center. This dates back to bias ply tires, and some techs are very slow learners.