Makes my boots fit
Having narrow feet, and I guess a narrow heel, I can never get my boots to fit right--even with advanced lacing tactics (and lacing them really uncomfortably tight on the ankles), I almost always have heel slip in any boot. The green superfeet are perfect, because they totally solve that problem for me. It also makes the boots more comfortable. I like them in mountain boots and I also like them in my nordic ski boots--ideally I'd have them in all my shoes, but it's more of an investment.