probably a really silly question!

I am interested in DRO - I was thinking that an ordinary PC mouse has
rotary encoders (two) inside it. The interface is already there to a
PC (the mouse cable) .. presumably all one would have to do is to
write some code to count movement and direction of the two wheels and
display it on the screen for a really simple DRO where the wheels
could be mechanically linked to the handwheels of a lathe -
Has anyone played with this? What would be the disadvantages?

Like I said - probably a dumb question but then I am a newbie!