Computer = All resources on the computer, Drive partitions, DBs, System State/Shadow Copy Components
Resource = SQL DBs, Lotus Notes DB, etc.
All = All
For our environment, we do use Resource only selection lists for our SQL servers. We back our DBs numerous times a day but we only backup the drive partitions once a day. Therefore, we have a selection that includes on the SQL instances (resource) and a selection list for the C and D drive (computer).
At least, that's how I interpret it. Hope this helps. :)
