Heres a little tip I thought I'd share. Some silly bugger shared it with me.
Take a carpenters pencil, a good graphite one, and draw a line around the joint where you want the solder to stop, solder/weld as normal.
Take care not to put too much solder close to the line, or it can physicaly push its way over.
Liquid paper does a pretty good job also and has the benefit of being able to lay down a thick line.
I always see polishing as time consuming, difficult, and generally unhealthy (I still like the result though). Anything to reduce polish/clean up time is a real help for me. You will need to passivate and clean the joint after. It's not the be all and end all, but it helps.
Of course, you wouldn't bother doing it brazing a joint in the dunny wall, but give it a go on your next "fine" job.