Depends on tradition. But in all tradition it has two important uses,
1) Wisdom ( occult knwoledge, pass test )
2) Apotropaic ( protection and exorcism )
Often used in exorcism potions ( brews , floorwashes ) or on pass test and wisdom oil, sometimes in success formulas , such as in Hoodoo.
Allegedly it was one of the ingreditents in mythical Cauldron of Ceridwen.
Someone well sugested using it in protective Circle forming / tracing. I'd mix
for such :)