As mentioned from others, it really depends upon the product using, the type of trim, and what's being done. Attached is a recent before, durring and after of a overspray removal on a black vehicle I was contracted to fix from a previous persons attempt (remove swirls, and wax from trim, cracks, & emblems). As you can see from the first image, textured plastic tends to suck up certain types of products. If I am buffing out a vehicle, I will mask edges and trim, period. It might take a few extra minutes, but the final results are worth every second. If I am waxing a vehicle, I am aware of which types of products in my arsenol that will tend to stain and if need be either mask or dress accordingly. I'll also note that for many of you outside California, solvent based dressings will work like a charm in preventing/ fixing these issues; unfortunatly due to EPA regulations, we don't!!