The point about ease of cleaning is a meaningful one, especially in any semi-finished or unfinished space. The amount of heavy dust falling onto the layout in such spaces is significant and will only grow over time without cleaning.
By not gluing ballast you remove the ability to use the good old "dust buster" from ones cleaning options. Clean track is happy track, dust attracts moisture which causes rust, dust get into grease and oil on cars and engines, and unless your layout is supposed to look like a pre-clean air and water act location with heavy industrial plants it can be a killer of what is otherwise a great layout.
There is a skill to gluing it down, just has one had to learn to use white glue in the 1st grade, one has to practice and learn to use it here again.
