Saliva or spit is used in the practice of hoodoo/rootwork/conjure primarily to bring a work to life via the symbolism of moisture. Spitting on powders that have been laid and spitting into a mojo bag are two common forms of using saliva in works. Saliva also has domination qualities and is used for enemy work. Perhaps the most famous use of spitting is the "chewin' the root", which is a work that is specifically connected to court case and legal work in which a worker will chew a root such as Little John, or else tobacco, and then spit on the floor where people will walk on the spittle. Another popular form is via mouth spraying in which alcohol and other substances are taken into the mouth by the worker and then sprayed over the body of the person.
Saliva is extremely powerful. Most people have no idea how powerful it is and it is wonderful for domination work. Ever wonder why so many adults, and especially mothers and grandmas, will use their saliva to clean a child's face? Well, at the same time they are reinforcing their role as being dominant.
I will share something with my readers that I have never read anywhere else online. My very first teacher taught me to use spit to dress my candles. That's right, spit. She didn't teach me to use spiritual oils. She mentioned that I could use them but she didn't teach me to use the oils. So for a long time spit was all I used to dress my candles. I didn't use my first spiritual oil until late 1993 or early 1994, and it was Anna Riva oil that I was first taught to use. To use spit to dress your candles you do everything as you normally do but when the point comes were you would dress the candles with oil you merely spit on it and then work the spit as if it was oil. Not only does the spit seal in the power and prayer and bring your work to life, but it is also your personal effect. Using spit to dress your candles is very powerful. I would just advise to allow time for the candle to dry or else the flame will sizzle.
Another thing that I've noticed is that workers don't seem to be spitting on their powders anymore. When you lay down a line of powders you call the person's name and state your petition and then you spit on it to activate it and bring it to life.