Are you talking about using sp_addumpdevice to create a logical backup device? For example, in SS2000 you might use
EXEC sp_addumpdevice 'disk', 'par_pos_1', 'C:\Program Files\Microsoft SQL Server\MSSQL$STATION9\BACKUP\wm_par_pos.bak'
...and then you would backup or restore by referring to the named backup device, instead of having to specify the full path and file name.
It seems to me that it would only be useful for developer backups and restores, because the file name is hard-coded into the device definition.