The gas does absolutely noting as far as "cleaning". They are inert gases used to sheild from impurities during the cooling of the weld. It really doesn't even do any cooling (put your hand oven the nozzle and tell me if you think the little that comes out would have any cooling effect!). Running argon over a surface before tig welding is a waste of gas. I find it hard to believe that someone who knows how to tig would even think this - especially a Canadian ;-) !!

Different mig gases will have an effect on a mig weld.