what does the wii motion plus do?

[Baelog]

What exactly does the wii motion plus do?

[BlackDS]

It makes the wii controlls work better, nuff said.

[Zidarose]

Much like Black DS said, it makes the controller work better.

What it does specifically is increase the number of axis that are tracked. It will notice rotations of the controller (play the Frisbee or Table Tennis games in Wii Sports Resort, and look at how your character is holding their Frisbee/Paddle) and better track the speed.