a superficial scratch will make no difference, a deep scratch can scatter light and cause artefacts. Often a Sharpie marker can fix it by colouring in the area scratched carefully.
on my FLs only one side needed doing as the swirl.marks caused a visible lack of sharpness. As it was fairly good value [£40 for the raw lens IIRC] decided to do both.
on my FLs only one side needed doing as the swirl.marks caused a visible lack of sharpness. As it was fairly good value [£40 for the raw lens IIRC] decided to do both.