[jacquesm]

Yes, this is called electrochemical cleaning. If you don't do that then the weld will be more vulnerable to oxidization because the protective layer that forms on stainless steel will be damaged and upset by the welding process leaving some of the iron in the steel directly exposed to the environment. This then can cause pitting of the surface, which is the beginning of the end.

For such a process to be effective it has to be done immediately after welding. You can use it to try to repair something that is already rust damaged but in my experience the gain from that is mostly a stay of execution, not a perfect solution.