Makes nicer code
I guess we're doing it for readability in sacrifice of simplicity or performance which admittedly is probably meaningless here.
If that's what you're after I'll happily accept the patch but I'd first like to know.
You can iterate the priorities then you don't need to create teh QList<QString> at all.
Here the right thing to do would be to iterate through facilities rather than the facilities keys and you'd save instantiating the list.