Simple answer: Because someone bought it for me.
But it's nice not to be totally limited in the distance that the CPU unit has to be to you.
The mouse on my main PC is still a wired one though.
The keyboard is wireless though... It was the only one that had all the features I wanted at the time, so I went RF. I probably would have bought the same keyboard in a wired version if the store had it at the time.
But again, it's just nice being able to place it anywhere on my desk and not have to worry about yet another cable run, or putting strain on the connector trying to get 'just one more inch.' Plus sometimes if I'm typing a long message out, or navigating something with only the keyboard, I can just put it in my lap and lean back in my chair.
Native XWA.Netter (Nutter?)