I recently worked with a chef who loved to use her vintage cookie sheet, passed down through several generations. There may be nothing wrong with old beat up cookie sheets. Lately, however, I have been thinking that it may be time for me to get new ones. No matter what a recipe says, the baking time will be slightly different for the one with the light vs. dark finish. It becomes problematic to use both of these at the same time, if baking a double batch in a convection oven. Mine are also insulated - with a pocket of air between two layers of metal. When I bought them years ago, they were very trendy. Now it seems that they do not fare well in equipment reviews, and books on baking are no longer advising their use.
America's Test Kitchen conducts extensive reviews of kitchenware. They preface their report with "Think your choice in cookie sheets doesn't matter? Think again. Most of the ones we tested ruined our cookies." If I ruin a cookie, I am inclined to think I did something wrong - but maybe it is the cookie sheet... The winner of their tests? Vollrath Wear-Ever Cookie Sheet (Natural Finish) which can be purchased from Amazon. [Update: I finally ordered two of these and they are wonderful!!]
Cookie sheets are not the same as baking sheets. The latter have rims that tend to block hot-air currents in the oven. As a result, baking time can vary (take longer) by up to three minutes, so bakers prefer rimless cookie sheets. (Home bakers who have only rimmed sheets should note the likelihood that the baking time will be a bit longer.) Rimless sheets usually have a small lip for grasping the sheet, but the absence of rims makes it easier to slip cookies on parchment off onto a cooling rack. Baking sheets with rims are sometimes called jelly roll pans or sheet pans. They have many uses, so it's useful to have both cookie and baking sheets..