Denny, I can tell you specifically what type of lautering system would benefit from letting the grain bed settle: mine. I have a pair of original Zymico Bazooka T's in a 70 quart cooler that feed a central manifold in an H configuration. Were I to add sparge water, stir, and "let 'er rip" there's a 50/50 chance I would end up with a stuck sparge. So allowing the grain bed to settle and develop is necessary for my system. A grain bed that is given time to settle creates a natural filter and is advantageous in a couple ways.
First, it allows the sugars in the grist to dissolve into the liquid, time is a factor in solubility of sugar in a liquid as it reaches concentration equilibrium between the grist and liquid. This is a minor concern as the value is low and on the homebrew scale nearly negligible. And while I have noted a 1-2 point increase in efficiency when allowing 5 minutes to pass in order for the grain bed to establish, (years ago when I noted every time, temp and volume), the more significant result was and is consistency in efficiency.
The second advantage is clear beer. Using the grain bed as a natural filter does just that, filters the liquid extract for clear run off into the kettle. A vigorous boil, quick chill, and after 2-3 weeks in the ferementers I rack directly into the keg(s) and my beer is crystal clear from day one. No cold crashing necessary. This is rarely the case when I use my small-batch mashtun, a 5 gallon round cooler with a SS braid, and with that system I don't wait for the grain bed to settle. Those beers have always needed time to clear.
So again I will state: it depends on your mash tun/system set up. Seems obvious not everyone is driving the same car.
david