The advanced temp folder configuration window allows you to specify an alternate temp folder path for use by your backup job.
You will not need to use this setting in the vast majority of scenarios. However, there may be cases where you wish to present a different temp folder path to SQL Server during backup operations.
For example, if you're running SQL Server on Ubuntu Linux machine that's accessible to the SQL Backup Master host, you can use this option to facilitate remote backup operations. In this case, you would create a temporary folder (e.g. "/home/user/dbtemp") on the Ubuntu machine for housing database backups and share via samba. In SQL Backup Master, you would then specify the samba temporary folder share location using UNC path notation (e.g. "\\ubuntu\dbtemp"). Since the instance of SQL Server running on Ubuntu will not be able to access this UNC path, you can specify an alternate temp folder path (e.g. "/home/user/dbtemp") for use specifically by SQL Server.
When specifying an alternate temp folder path, keep in mind that it must resolve to the same location as your primary temp folder path.