In a match, I wipe frizzen,rock,and pan in that order with one of those prepackaged alcohol wipes between every shot. I know, I know...compared to some folks, that might be considered just a little much..it's not necessary, etc. I want every shot to see the same conditions. That applies to every aspect of the shot...ball, powder, patch, barrel condition (i.e.:level of fouling), amount of compression AND..ignition.
Shooting in high heat and humidity in South Georgia and Florida a lot of wet crud accumulates. I have no idea how long I could go without wiping, and don't feel the need to find out.