LB
For a flight to a destination for which a prescribed instrument approach procedure does not exist, the minimum requirement is a GAF.
That is under the Flight Planning Preparation - Forecasts section. So I just interpret that to be if when I am looking at my briefing package I can use a GAF.
To me that is different from the subsequent section which deals with Alternates. Which, as CN said, states emphatically No TAF = Alternate.