I don't fly the 'bus but, if the FDs are providing vertical guidance on the Baro-VNAV path and (pretty accurate) lateral NAV guidance, why wouldn't you leave them on?
+1
Again drifting to Boeing but if the profile in the FMC ties in with the published profile we generally leave the FDs on, with the usual caveat/briefing about handling any possible mismatches with any VGSIs due to temperature.