I find it depends on how you treat the pads when detailing as well as what products you use. My finishing pads, some of them have done up to 20 cars and are still happily trucking on. But these pads aren't really worked hard. My 4" spot cutting pads only manage a car, just, using a high abrasive compound like
Menzerna Power Gloss.
I also find watching people that if they apply far too much pressure to the PC (or rotary), then they will eat through their pads faster as well.... Lots of variables, but for cutting pads I have some that are now ten cars old and happy from the rotary, and the PC, but I tend to bin them at this point as a matter of course.