As others have noted it should be off by default. But I can see it being useful for things like posts with pretty pictures when you're on vacation.

One approach would be to gather data (stored locally) that figures out locations where the person often is and have a "Are you sure?" prompt if they're in one of those locations. It's one thing to geotag a post in a place where you rarely are. It's another one to geotag a post with your home location.