Also, in any conditions, in CAS even, there could be traffic there which isn't supposed to be there - as some have found out.
One is more likely to encounter it if the actual conditions are VMC, obviously, for that is the profile of the GA population, but one could be going down an ILS where from the FAF down to the DA one passes through 2 or 3 cloud layers, and somebody flying "VFR", or even just busting CAS, could be perfectly happy with themselves flying between the layers.
If you are head down all the way, and single pilot, and absolutely obeying the company rulebook and not even lifting the eyebrows to see if you are visual until the altimeter reads the DA (which I completely believe Timothy was doing, but it beggars belief that it would really be standard practice because it goes so much against human nature and self preservation) you are denying yourself the opportunity to spot some joker.
In VMC conditions you are chucking away the chance of spotting a runway incursion nice and early, or a helicopter doing something at 100ft AAL, etc.
But hey company policy is company policy no matter how weird. I once asked an instructor if when he was flying an NDB approach, and the ADF was indicating OK but a GPS was telling him he was about to die, his reply was he would trust the ADF.