I'd say I travel on average four or five times a year. This, combined with an obsession with taking as much free stuff as I legally can (something I was never able to shake off, even long after graduating college), has resulted in a LOT of mini shampoos.
We always pack a few with us when we travel -- y'know, just in case we end up stranded on the side of the road and need to fend for ourselves when it comes to personal hygiene. But we never end up using them.
Before, I just kept them in a giant grocery bag in the bathroom closet. But why not put them to use? If you have a guest bathroom, a glass jar with the mini shampoos is a nice way to accent the room and provide guests with the necessary hygienic products without lining the bathtub with gigantic jugs.
Granted, my "guest bathroom" right now is also the "bathroom that's not connected to our bedroom" -- also the only bathroom that has a bathtub/shower, so the function is kind of moot. But someday -- someday -- this will be incredibly useful when we actually get a house.