Ideally CNF is written against Total WL / RAC - Current WL / RAC.
Actually I want a LB seat, chances are good if its RAC / WL, and on charting at least 1 berth would be lower.
If it directly assigns a UB / MB, then it will be waste.
Also, if 1 is given confirmed seat, the next passenger on that PNR...
more... may get confirmed accommodation in other coach as well.