If you do a search....youl'll find they keep the bars from tankslapping or mving side to side quickly.....You'll usually wish you had one accelerating hard over rough pavement or bumps in the road or when your coming down from wheelies:rock
It's kind of like suspension for your steering. Or maybe a seatbelt for your forks, sometimes when sportbikes with radical steering geometry and high horspepower mix the front end can weave/shake. As far as always needing them this isn't true. You can ride R1's fine without a damper. But if you like giving it lots of gas out of real slow corners/over rough pavement or doing wheelies, they can save yourself a little trouble.
thanx alot for your replys. i saw one of those videos on this site when the guy lost control and the front end was weaving crazily and now i know where it can help cause he crashed pretty hard. thnx again-matt:jump