Dyrian525Being closer to your mouth it'll pick up less background noise, and reproduce your voice more clearly, and unless you have an $80+ webcam, the sound quality in general will probably be noticeably better.
It's not really intended for webcam users though, the main selling point is for people who want to turn their good headphones into headsets for skype calls or multiplayer gaming, or any other situation that would make a desk mic impractical or undesirable.
Dyrian525Using a mic that's closer to your mouth is going to, ceteris paribus, sound clearer. Add to that a higher quality mic and there is a huge difference. Plus, the mics that go into webcams, are not always of even decent quality.