Clyde Ranthal is in a hidden valley, very much out of the way from normal travels. Everything he sells is much easier to obtain elsewhere, and he would have no impact on the game, except, he is the only source for , which teaches leatherworkers how to make .
This is a good, but not great, pattern. can be learned from the leatherworking trainer, and is nearly as good and much cheaper to make. Several +3 stamina cloaks drop and are frequently for sale in the auction house. is often a better alternative.
He only sells to Alliance characters. It is doubtful that he ever drops the pattern. Horde characters can obtain this pattern when an Alliance character puts it up for auction on the neutral auction house.
Because he is the only vendor and the pattern is limited supply, demand exceeds supply and this pattern can sell for quite a bit. If you want to buy his pattern for resale, consider logging out near Clyde Ranthal, playing another character, and checking periodically for restock.