sourcecow is really orientated more toward the person starting out on twitter vs the person with an established 500 followers/friends. the plugin detects a "follow" event on twitter and window appears the moment you follow someone, at that time you're asked 3 questions, why, how you found them, what you hope to gain by following them.

without a plugin or a way to hit the person at the moment they decided to follow someone you'd have to care to come to the site and tell why afterwards etc. the plugin just facilitates the "get'm now while its hot in yer head"