I often see questions online where someone wants to find out who started a trace, when tempdb last had an autogrow event, or when the last full backup for master occurred. Since these and other events are captured by the default trace, but the default trace only keeps five 20MB rollover files by default. This means that the event you are after may no longer be there, depending on how long ago it was and how busy your server happens to be. Unfortunately, people often need to find this information well after the fact.