If our documents were perfect, there would be no need for order of precedence. But in the real world, setting an order of precedence does have merit, especially for bidding.
For example, it seems reasonable that large scale drawings would be more accurate than small scale drawings. That was certainly true in the days of hand drafting, but is often true even today, when CAD gives the same accuracy at any scale. Contractors are told not to scale drawings for takeoffs, but many times dimensions are not given or are difficult to find.
Quantities stated or implied frequently vary between specifications and drawings, and sometimes within either. I have often seen landscape documents that showed trees graphically, included a quantity schedule on the drawings, and specified quantities in the specifications. In most cases, at least two of the quantities are different; I recall one project that had three different quantities for the same plant.
Yes, the bidder is required to notify the architect of such discrepancies, and no, I dont have much sympathy for those who dont. The problem is that you cant know if the bidder didnt see the differences, or did see them and filed them in the change order file. The benefit of order of precedence is that it establishes a starting point for the inevitable change order.
The disadvantage is that the result does not necessarily agree with the intent. Requirements such as bid the greater quantity or the more expensive product, which essentially establish an order of precedence, are a commonly used attempt to overcome discrepancies in the documents.
If a claim does result from a discrepancy, my observation of case law indicates the courts will favor the contractor, who had but a couple of weeks to figure out what all those drawings and specifications mean, over the design professional, who had months to prepare them. Again, if we produced perfect documents there would be no problems.
I am not arguing in favor of an order of precedence, just commenting on the reason for doing it. In the future, this may become a non-issue, as the integration of CAD and specification software will go a long way toward eliminating conflicting information.