The Stick allows you to self massage to pretty much any part of the body. Massage increases circulation and helps reduce muscle "knots". After a long days walking, skiing, climbing or any other physical exercise a massage can reduce muscle soreness and discomfort.
The Travel Stick (red handles) shortest version of the stick and therefore more portable. Great for use on the legs but not as easy for the upper body, popularized by the USA Cycling team.
It is easy to be used by yourself on all major muscle groups.