The Olfactory Sense of Desire allowed Sorath to connect with and sense the very existence of something he desired, no matter how far away it was. If what he desired existed, he could definitely find it.
It was a perception ability which worked on a different principle to normal Unrestricted Spells used for searching, and it was also more exceptional than the simple ability of Crimson Denizens and Flame Haze to sense presence. If what Sorath desired was there, he could even feel things within the concealment spell Crypta, which cuts off all presence. However, Sorath usually got bored and threw away the things he had desired after obtaining them.