I can not remember the last time I used it for a serpent...... But I use it for trapping trolls, lox and wolves. Also it is fun to harpoon flying enemies (drakes and gjalls). You can still use your bow while it is harpooned, or drag them to an adjacent biome to fight other mobs. Dragging a gjall into mountians and watching 2 drakes take it down is a pleasant diversion.

Just remembered a time it saved me. I was alone on a multiplayer server and got stuck in one of the little water tunnels that go nowhere in a crypy. Deep enough to drain stamina if I moved, but I couldnt get over some root or something under the water. I logged out, called my brother so he could log in. He showed up with his harpoon, we turned on PVP, he harpooned me and pulled me out. I was very happy.