I love secondhand yarn. My taste in colors is never the same as someone else's, and when I receive a big bag of yarn that I didn't pick out, it gives me the chance to work with materials and shades that I would never have chosen myself. I don't have the added stress of "I can't use this for a silly project, it cost $$$!!" because, hey, free yarn!
I'm seeing some interestingly plumed tiny owls in the future.