No, this is not a new version of two-finger-typing for those endowed like Cyrano de Bergerac. It is about adding a new layer of reality and depth to your setting and scene description, and about playing up the differences between characters.
Scent may be one of the senses least invoked in writing. When we describe a setting or individual, most of us start with physical characteristics (visual), then perhaps the sound of their voice or the sounds of a place. Then the personality, the overall emotional sense “feeling” of the person or location. Taste and smell come farther down the list, for good reasons. Unless you are writing about a chef, a professional “nose,” or a geologist, having a character think about taste and flavors may seem a touch strange. Having the protagonist taste people…. eh, unless you are doing something a la Silence of the Lambs, or some erotic scenes, probably not recommended. Touch likewise, although a pet owner (or mage with a Familiar) who hears that sound in the night and realizes that it came from between him and the light switch, and he has to get up to deal with the problem, and his foot touches…
Why geologists and taste? Is that gypsum or some other salt-rich mineral? Geologists around here seem prone to cleaning off samples and touching them with their tongues to verify mineral types. YMMV, and biologists do not do this, by in large.
So, what scents, and why? We are all familiar with someone who always used a certain perfume of aftershave, so much that it becomes difficult to separate the scent from memories of the individual. My great-aunt, the Southern Belle in the family, used Royal Secret. If I could find a bottle, I’d grab it in a heartbeat because of the memories that it evokes. There are also scents of times and events, like someone’s fresh-from-the-oven breads, or roast meat (turkey or goose or duck). Perhaps lemon trees from an especially memorable summer vacation, or the smell of the sea and first teenage love during a trip to the beach… Scent is visceral, tapping into something very old and strong in most people.
The absence of a scent can also be a warning. If you have a fantasy species that uses pheromones to communicate, what does it mean if an individual doesn’t produce a scent? What if a flower or other scented plant is not blooming when it should? Has someone been working forbidden magic? Or does your protagonist groan because it is the early warning that they need to get ready for early onset allergies or the Return of the Son of the Revenge of the Head Cold: Part Three the Sequel. I imagine that space ships and space stations smell metallic and a bit stale because of recycling the atmosphere. Or is stale a bad thing because it means the scrubbers have begun to fail and they’re dang near impossible to reach without taking the entire system apart?
The topic is on my mind in part because of working on a fifth Shikari book, and because of editing Miners and Empire. Part of the story takes place inside a mine, and wet mines have a certain scent to them. If they are “breathing,” it can be a good, familiar scent that means the old air is being pulled out and fresh drawn in, or it could be bad, with CO2 or flammable gasses starting to filter up from the lowest galleries. This particular mine, and the real one it is based on, smell a bit of chemicals and rock, because they are lead/silver/copper mines, with some iron and vitriol. The mine is not a wet mine per se, but it does have water in it, and so smells a bit like wet stone and metal. For the character, these are normal, healthy scents, a little comforting because it means there are no miasmas lurking where he intends to work. On the first day of the work week, the mine smells a little of smoke as well, because fire-miners have been at work cracking the rocks. The character also knows the smells of a medieval town, and what he should not smell.
When used well, scents pull the reader deeper into your world and make it more real. How real? that’s up to you. I’d just as soon only imagine what the area around an angry 100 lb skunk smells like, thank you. And you do not have to describe in detail the smell of human death. I know that one already.