Burrs on the edges of stampings can cause problems because they prevent the part from seating properly or the burrs can break off and become particles which can be expelled during the welding operation.
Burrs which hold the parts apart frequently will collapse when current is applied since they generally will be carrying an excessive amount of this current. This excessive current in fact causes these burrs to become expulsion particles and dangerous sparks in the work area. Even the burrs which break off during the squeeze sequence can become expulsion during the weld operation since they are merely lying on the surface of the part.
The goal is to reduce the burrs being produced by your stamping operation.