I dunno, good question. Maybe something like this: there's some cases where I'll prefer cookies to session data, esp if it's non-volatile data that I can take or leave, like convenience values for the user on the js side, "last selected item" or the like.

I don't necessarily want that data in my session, or as a user attribute that I have to migrate the DB for. If it's a pkid or something that isn't necessarily sensitive, but I also don't want it to be too easy to get at, I might use a signed cookie.

Now, I've never actually done this... ;p