Snot building also becomes an option below the “surface” to have interesting texture, like mosaic floors, brick built road incorporated on a plate, deep sewer drains along sidewalk, etc.
In which case MILS is not “adding nothing”, it is adding the ability to build below the surface. Which is why I use it for my town sections; it adds depth and a layer of detail that a flat baseplate can not.
If we find that we are having sections of displays MILS’d and other are not, we could work on some “transition” sections to gradually bring the MILS’d level down to the flat baseplate level. That would look better than an abrupt transition from MILS to non-MILS.