Very useful for when you're stuffed up, have a headache or are just feeling like you can't get enough air. Also useful for reminding your body to breathe well if you're not doing great mentally, though any strongly scented thing would do this.
Do be careful to not get it on your hands or nostrils. I like to hold a cotton wool pad over the bottle opening, as it makes it easier to inhale deeply, but even this you should avoid touching.