Pits are bad.
Cartridge cases are gas seals. They also allow the powder, propellant, and bullet to be packaged, but I take that for granted. Case head brass thickness and quality is safety critical. Rupture the case head and all that gas comes out into the gas and busts things up.
This single heat treat 03 blew a case head and sent the owner to the hospital.
Tarnish on brass has been no big deal in my experience. But any pitting that reduces the strength of the brass, or corrosive chemicals (ammonia) that weakens brass, it is not safe to use.