If it was galvanised, or any form of plating, I would always remove it prior to any form of heat jointing: otherwise the weld would have included slag and be very weak, whether Gas, Shielded Arc, Spot, High Frequency Resistance, MIG or TIG.
Still, I suppose that leaves Pop Rivets..........................
I once saw an insurance write off (MG 1300) here both wings and the front panel had been popped on in place of spot welds.
When the owner hit something, the whole front end apparently sort of slid off up the road!
The guy didn't even have the brain to use steel or even Mono Metal rivets: just plain old 1/8" ally!
Which, well sort of corroded: as they do.
Made me larf!