That depends on aisle spacing. A four post box has some dimension.
Depending upon the aisle spacing, it could obstruct an aisle or
obstruct access to other equipment. Midmounting works great in properly
sized aisles with defined "working sides" etc.
I hate it when I catch something on a box that should be in a cabinet
but for some reason it was midmounted when it shouldn't have been. It
is kind of dangerous, especially if it's eye level.
-M