Hi Ron,
I don't think a back action lock has any advantages with respect to performance. However, according to Howard Blackmore (British Military Firearms 1650-1850), the famous Enfield master armorer, George Lovell, designed a back action lock for the new percussion rifles and muskets that would replace the flintlocks. His rationale for the change from a more conventional sidelock was that the back action was lighter and required fewer parts, and thus was cheaper to make.
dave