its not about painting the whole car its about blending into the doors because otherwise the front half of the car is going to be night and day... Also by putting the sandable primer on there it has caused more work because that crappy stuff reacts badly 90% of the time with real primer sealer or basecoat causing it to lift or(wrinkle) so it is recomended to sand it completely off. Ask oldschool98 he was looking to do some cheap work