There are several uses, but generally Br/I is sensitized with Au/S and Cl and Cl/Br are sensitized with S only. This is a broad generalization.

Au tends to make Cl emulsions have very soft toes and high fog. Treatments patented by several workers devised methods of using Au/S on Cl and Cl/Br emulsions. That was only in the 70s.

PE