Maybe the easiest answer to "how important" is - 'not much'.
Read reply #11. If you get down to VOR/VOR updating, which I don't think I've ever(?) seen 12,500+ hrs of 'PFM' operation, you'll probably have gone through a couple of checkslists that probably will tell you to ensure that VOR updating is in the 'auto', 'on' or 'enabled' mode.
PFM? Pure F***ing Magic.
It's a DFW system. DFW? Don't F*** With it.
