1. The sense of smell is the only one connected directly to the limbic system, the part of our brains which govern initial emotional and sexual response. Smell then goes on to stimulate the cortex, which allows us to recognise it on a concious level - but long before this we have already made our emotional reaction.
When we meet a lover, the first sense to register the pleasure that comes with this is the sense of smell, for this very reason. Perhaps, then, if you are wanting to make a good impression, there can be no better consideration than the consideration of how you smell, as opposed to what top you're wearing or how you've done you're hair.
2. Smell exists almost exclusively in the moment. We can remember and recite chords of a song very easily, and can mentally put together simple visuals without too much trouble - we're even, to some extent, able to recall the sensations of touch, even enough to make our tiny body hairs bristle appropriately. But smell is notoriously difficult to recall, granting little more than vague approximations, incomparably weak compared to the actual real life sensation.
This is why, I suggest, smell is an oddly useful sense in the staving off of depression and general anxiety. So much of depression and anxiety is perpetuated by the inability to live life in the now, and instead dwell over the past or worry about the future, thus allowing our at times brutal imaginations to run riot on our hypothetical lives. The experience of smell forces us to exist within a single moment - we can recognise and remember the experience of smelling it, but our recollection does not allow us to even remotely recreate this rich feeling. Nor, do we miss smells - it is akin to a death of a dozen thousand of Cupid's arrows in the back to smell a former lover's scent, we will not generally consider the smell when we have no access to it - we will not miss it (though we will miss their warm presence in bed and clever, articulate eyes), and now will we fear it (though we will fear the sound of their disembodied voice from behind a telephone reciever).
In practical terms, smell could be useful for a sufferer of depression and anxiety to simply learn to ignore the shame of the past and the nightmare of the future and simply posit themselves in a fragrant now. I am not suggesting smell is a magic bullet to happiness, but rather, it could be very useful tool in training our minds to simply be, rather than simply implode in panic and despair.
To try and see, why not next time you're feeling overwhelmed, just run a bath with a few drops of some essential oils - a good, and oft repeated blend is a few drops of bergamot, a few drops of lavender and a few drops of cedarwood - and just concentrate your mind to just dissect the smells.