Agreed. We tried to eat at Boatwright's at POR twice on one recent trip when staying at POFQ. We walked up, saw the restaurant was nearly empty, and tried to be seated. We were told it was ADR seating only. I protested that there were maybe 3 tables in the entire restaurant that had people sitting at them, to no avail. We made the ADR (because it was too late and we were too tired to leave POR/POFQ to find another restaurant), had to make it a minimum of 1 hour later due to ADR policy, explored POR a little bit, came back and were seated. As it was an hour earlier, the restaurant was still nearly empty. It was a good meal, but would not have been possible at all without jumping through the ADR hoop. We went there again later in our trip because the meal was so good, this time with an ADR, and this time with the ADR just as unnecessary if it were any restaurant outside the WDW bubble.
So in this case, not only was it advisable to pre-plan for a desired meal, it was actually 100% necessary.