Fragrance in plants is a multi-faceted story. I never fail to stop to smell the 'Gertrude Jekyll' roses when I walk by their flowers while at work. And I still mourn failing to move some peonies with me that were so fragrant their cut flowers could perfume a large room. In retrospect I never appreciated how rare that intense fragrance is in peonies. On the other hand I am repeatedly irritated by claims of lovely fragrance that in-truth require deep inhalation with nose squarely imbedded into the flower. And, of course, there is the long established kvetch about breeders neglecting the fragrance trait in otherwise fragrant plants like roses (and peonies, I suppose).
The sense of smell powerfully influences our memories and can bring back long forgotten experiences. The smell of petunias, which is more distinctive than fragrant, immediately brings me back to my early childhood.
Fragrance can transform an evening. For example the smell of the flowers of Brugmansia (Angel's Trumpet) brings back an early evening walk in Balboa Park in San Diego. As I was walking along I was suddenly aware of a most wonderful fragrance which I was able to trace back to a Brugmansia tree. The flowers that emit their strongest fragrance in the evening bring a special delight to what is probably the most emotion laden time for visiting a garden. Nicotiana sylvstris, flowering tobacco, is another memorable plant that contributes to the pleasures of an early evening in the garden, and night-blooming cereus is worthy of a special evening pilgrimage to an enlightened greenhouse.
Another sort of fragrance experience is provided by the likes of Abelia mosanensis (Fragrant Abelia) and Viburnum carlesii (Koreanspice Viburnum). These two shrub's fragrance can transform an entire backyard. Curiously around my part of the country the Abelia most often seen is Abelia x grandiflora, a half hardy shrub with forgettable fragrance. (I really can't recall.) On the other hand Abelia mosanensis is fully hardy and made our deck a sensory delight for about two weeks this spring.