Kendra Little explains the importance of tail log backups in the course of answering a reader question:
When you restore a full backup, does it restore to when you started the backup job— or when it completed?
In this episode, I give you the super-short answer. (Spoiler: a point near the end of when the backup was running.) For the full answer, complete with a detailed timeline to help you understand the nitty gritty, read “Understanding SQL Server Backups” by Paul Randal
Click through for the video as well as a bit more information on tail log backups.