C indicates that limits should be copied from the old contract to the new. In this case, the effective dates on the limits are changed to reflect the start and end dates of the renewed contract. This is the correct choice if you have created limits that are unique to a particular contract, or modified limits copied from the service type.

S indicates that limits should be copied from the contract type, just as when a new contract is created. This is useful for organizations that want to phase in changes by setting them up in the contract type using effective dates. During renewal, the limits that are currently effective for the contract start date are brought in.