The main reason for using hydropel on the feet was as a water barrier, particularly in wet weather. It prevented skin from becoming water logged and nipped problems like maceration and blisters at the bud.
Even with hydropel good foot care practices are important like socks, proper fitting shoes, well groomed nails, keeping calouses from getting too big, etc.
edited: Wanted to make this more feet specific. Nicks' points above, and in the article, about problems in the groin area are very good.