I went to culinary school in Japan, where we almost exclusively used Aluminum cookware (extremely rust-prone). They forced us to scrub the pots almost every week with Brillo pads until they were bright and shiny. The reasons they used to gave us (aside from the prettiness) was:
1.) Tarnish causes rust which causes pitting.
I think the teachers also believed the tarnish would affect the color and taste the food itself. But then again, they were like super-perfectionists.