There are somewhere between 700 and 900 different types of Salvia or sage, lots of differences between different plants in that genus. I did some digging on clary sage recently and bought a small bottle of the essential oil.
It's traditional uses in aromatherapy include promoting mental clarity, opposing anxiety and depression, an aphrodisiac, relaxing muscles and reducing spasms, bringing on menstruation (among other things).
This article found that it acts on the dopamine receptors, which are associated with reward/pleasure - that could explain some of the effects on mood.
This may be a resurrection of an old post, but as I was doing some permaculture homework, I came across it.
I recently visited the Permaculture Institute's demonstration site in Santa Fe, and encountered clary sage there. Just based on the information that our tour guide gave us, and a cursory internet search, here are the differences as I see them.
First, clary sage is a biennial herb and not perennial. Rather than forming a small woody shrub (officianalis), it produces a low lying rosette its first year, and then shoots a flowering stalk the second year. Depending on the variety, the flowering stalk may produce white (Vatican variety) or blue-purplish (turkestanica variety) flowers. Both the leaves and flowers are useful in teas, and the oil from the flower is a popular essential oil for aromatherapy.