I don´t know if users really change or (de)activate often symbols or captions.
Me neither, but I had often requests that those symbols/captions are more important than others and vice versa, so now one can choose which to show (it helps a lot with symbol/caption elimination, too). I usually assume that people know better than me what they want so having the option to get closer to it isn't hurting.
Probably most of the time users set their overlays only once, but there are other cases:
I sometimes use the routes in the maps for hiking/cycling and now can switch on strong overlays for those, and sometimes I don't and can deactivate routes altogether. Or I usually don't need to see hospitals in a city map, but in emergency I only want to see those (OK, there are other solutions for that in Locus now).
Changing the whole theme with Locus is not much more work for users.
Depends on the user ;-)