It gets your mouse closer to the actual keyboard.

When you let go of the keyboard to get your mouse with a full, you have to go over to the numpad, even though you don’t use it very often. It puts your right hand in a position that’s not very natural, at least to me.

I guess that’s the biggest hurdle, especially when it comes to social apps. One tech-savvy person wanting to migrate is usually not enough to start moving a community, even as a small as a group of friends.