That would be a nice enhancement. It could be just like downloading maps, but in reverse: after selecting the area, Locus, gives you the list of tiles per zoom level in that area, and you select the zoom levels you want to delete.
For example, I have just downloaded from Google the cities of NY and Miami (because I am going there soon) in great detail, plus BRasil and some areas in it in less detail (bacause I live in Brasil and travel a lot

). I wished I was able to delete only the portions for NY and Miami (about 150MB each) , without having to deleted the whole Google file (which has some 150MB relating to Brasil and other stuff).
Rodrigo