Smell is a direct, unfiltered sense. Odors, perfumes, stinks are immediately perceived by our sense and goes directly to the brain. Obviously such a great faculty should have its magickal counterpart, and in fact, early records prove the great antiquity of the sacred and spiritual use of incenses, herbs, resins and perfumes.
Fumigations of strong smelly and pungent resins and herbs, in mixtures or alone, have always been used for driving away all sort of troubles, evil Spirits, demons or baneful energies. On the contrary more sweet smelling odors are burned to deities, spirits, angels etc as an offering and also a way to call them.
In the Holy Bible, Exodus 30-34, was given the Moses an exact recipe of mixed incense resins exclusively for divine worship. Spices as well are added accordingly to the purpose of the magickal operation.
Incenses are a gift of the Vegetable Kingdom of Mother Nature. There are resins (frankincense, myrrh, copal) plant parts like dried flowers (saffron) or leaves (sage, lavender, sweetgrass) , roots (ginger, high john, galbanum), barks (cinnamon, sandalwood, seeds (star anise) or juices (sugars). Sometimes essential oils are added as well some animal parts like powdered bull or buffalo horns, snake skins etc but more rarely.
Incenses or sacred mixtures are released in the air by flames. Fire activate their properties fueled by prayers, enhanced by the proven efficacy of an old recipe. Definitely they are useful and powerful tools in the arsenal of Hoodoo-Conjure-Rootwork.