Because Backup and Migrate sorts files by age, when you untar or copy some files to a destination, they will be more or less the same date and it may be hard to tell which ones are the latest etc. This makes it necessary to create a file pattern with the backup date at the start and make sorting by file name easier.
PS. Getting the date of the files restored from the archive correctly can be accomplished by some of the tar options.
On the Advanced Backup options page below the Backup filename there is a link Replacement patterns which expands to display another link Current date which displays some of the tokens available. None of the existing ones suits my preference which is a numeric date.
Using the PHP date options a good date prefix would be [current-date:custom:Ymd-Gi] or [current-date:custom:Y-m-d-Gi] the latter resulting in a string like '2013-11-17-1924' for 17th November 7:24 pm.
As an example I have a Backup filename token [current-date:custom:Ymd-Gi]_[site:name]-PMU, the PMU meaning Pre Module Update, something to use just before upgrading modules so you can revert the configuration if something goes wrong
