The difference would be that [Table].[Column] works, while [Table]..[Column] doesn't. At least I've never used syntax like that and I don't know of any reason why it would work.
I think you are getting this confused with table references, which may or may not include the object owner's name.
The full reference for an object (such as a table) is:
...but if the object is in the current database you can simply refer to it as
In either case, you are allowed to omit the owner. SQL Server will search first for an object owned by the current user, and if it cannot find one then it will search for an object that is owned by DBO:
If it's not practically useful, then it's practically useless.