When? When using systems with a snapshot and the Active Directory requires updating the computer account password.
Why? Active Directory is normally configured to have the computeraccounts updated every 30 days for security reasons. This policy can be changed, but sometimes you don’t have the control over this policy.
Tooling? In Windows 7 and Windows 8 the command “nltest” is part of the operating system. On older versions it is located in the Resource Kit.