After all, the cream of tartar works much better when it hasn't aged out of usefulness. Spices do not have an unlimited shelf life, and it's nice to know if the cardamom you're about to put into that cookie recipe is from 2010 or 1996.
I started labelling the lids this summer, and it's been a huge help. Not only do I know when I opened something, but now I can also gauge how fast I go through something. Example: if I'm plowing through an 8 oz. bottle of clear vanilla extract in three months, then I should consider buying more when they are on sale, or purchasing a larger size. Like in a five-gallon bucket. Just sayin'.