The last couple of mice that I've owned have had this feature, but I've never really considered that it'd be useful until a week or two ago. I like to keep my wrist stationary on the desk and use my fingertips to push the mouse around, so I can move quite a bit further horizontally than vertically. I have my dpi set to 3000 on the X and a blazing 5700 on the Y, and it's immensely more comfortable than anything I've ever used. I have no problem reaching every corner of my 2880x900 desktop setup with a great deal of precision at every point in between, and I never have to move my wrist or lift my mouse off the desk.