By default when a Peer Group is created that allows for password-authentication (or the password for such a Group is changed) Peer Grouping validates that the password meets the password complexity requirements for the local system. Thus it will not allow any passwords to be used for a Peer Group that are weaker than what would be allowed for a login password.This setting controls this validation behavior. If set to 1 then this validation will not be performed and any password will be allowed. If set to 0 the validation will be performed.
Network\Microsoft Peer-to-Peer Networking Services
At least Windows Vista