Boris_Badenov
Bongardo
Well if you register your games you can get coins to use to get rewards. Rewards include downloadable games or merchandise. The merchandise isn't really that great if you ask me, but I got some pretty cool games for free this way.
As for downsides I really don't see any, so, why not register?
I didn't want Nintendo to watch me do naughty stuff on inchworm animation.
I don't even know what inchworm animation is...
But either way I don't think they will be watching individual people doing anything.