[Marcello]

"Looks like you are mostly talking about lower human-scale berms here, right? Like ones used for low-level fortifications, e.g. around dug-in tanks?"

Mostly about the zillion of berms which are built in Iraq.
These do not typically include trenches and are used in a variety of places such as the national borders, to enclose coalition bases etc. Rough terrain does not block LOS nowhere nearly enough to be used in their place, they are much smaller than 50m and I guess they would offer some cover as defensive positions if needs be. I can do with elevation but as it has been said they would be a nice addition.

EDIT

They are also used as obstacles for vehicles (think car bombs but not only).Elevation does not stop 2WD vehicles in the game.