How, when and why do people use them? Obviously after claying and polishing (duh) but are they necessary prior to sealing or waxing? Can Dawn or or alcohol suffice?
It depends on the situation. I wouldn't say hey are necessary before sealing/waxing if the car is free of contamination (or other LSPs), but sometimes you don't clay/compound before you seal/wax, so if you have something that needs removing (be it another LSP, waterspots, etc...) chemical cleaners can make a lot of sense.
