IMHO, the FPV is very useful for all kind of visual approaches.
Addl: If u see the FPV and you or PNF has not selected it most likely FD and AP are not avbl.
You maynot have the FD but you will always have FPV.
The only time it fails, in addition to Pitot static as mentioned earlier, is if the selector button fails.
Very good for NPA (Rec Proc by Airbus) and esp transition to visual profile.