Singleton: How should it be used

Question

Edit: From another question I provided an answer that has links to a lot of questions/answers about singletons: More info about singletons here:

So I have read th

Answer 1

In desktop apps (I know, only us dinosaurs write these anymore!) they are essential for getting relatively unchanging global application settings - the user language, path to help files, user preferences etc which would otherwise have to propogate into every class and every dialog.

Edit - of course these should be read-only !