Comment 258 for bug 668415

Tablets, phones and some LCDs with pivot have portrait mode in which launcher on the left takes too much space and is ridiculously high. Tablets especially are often used in this mode. So if you want to make Unity for tablets you need to make it movable anyway. (and on phones it would have to be on the bottom anyway - most new phones are 16:9 and used in portrait with little space for launcher on the left)