In a word: Versatility
This garment exceeded expectations. Originally, I bought one as heavier underlayer to use instead of my North Face poly. After wearing it, I had to go back and get another one b/c it was so great. I use it as a heavier base layer but also as a lighter second layer. The fit is fantastic and my North Face polys are collecting dust now. It breaths, wicks, and does all the tricks. Only down side is it does get that poly smell more than some items, but despite what other reviewers suggest, all the wool bases make me itch and sweat. So Delta, you rock!