Does Size Matter?

When shopping for a new shampoo, facial wash, lotion, and other beauty product, what size to you usually get? Do you really feel that bigger sizes are more economical? Or are you uncertain if you can use up the entire product so buy just the right size?

I for one get the smallest size possible most of the time, not only because I don't like carrying the big one around the store, but also because I enjoy trying out different product lines from different brands. I only invest in the jumbo sizes if it's my favorite product or if there's a big price cut going on. What about you?