From "SQL Server DMV Starter Pack" by Louis Davidson and Tim Ford.
Report unusual conditions that may be filling up your transaction log. It returns the recovery model, log reuse wait description, transaction log size, log space used, % of log used, compatibility level, and page verify option for each database on the current SQL Server instance.
For example, if your log reuse wait description is something unusual, such as ACTIVE_TRANSACTION, and your transaction log is 85% full, then some action is probably required.