You use the log file any time you take a log backup, roll a transaction back, restart SQL and let the database recover, implement mirroring, transactional replication or CDC.
So what 'usage' did you have in mind that's not covered there. It's not an audit log if you're thinking of using it to see who ran what and when.
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
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