In my area, a regular 1/4 mile pivot will run continuous on corn or beans from around the middle of June until August only shutting down about a day for 1 inch of rain.
This is drawing back on some agronomy from college 15 years ago, but I believe that corn during its peak water usage time (around tasseling) can use as much as .5 inches of water a day depending on temperature etc. Most 1/4 mile pivots around here are only capable of about 1" of water on a 3 day pass, or .33 inches per day on a 800-1000 GPM well. (These are approximate numbers, you could calculate the acre-inches of water for 1000GPM times 72 hours etc, but that would be too much work
) This means there is an amount of time in which you can not physically put enough water on to keep up with the corn, but if you have a full soil profile, it will be able to make up the difference. Any help from Mother Nature is a bonus, but that is why you turn immediately back on after a day, even after a 1" rain.
Now, I have not run a 1/2 mile pivot, but in order to apply the same amount of water to 4 times the area, one could assume you would need to either apply 4 times the volume for the same amount of time (3200-4000GPM on 3 day revolution), or slow down the pivot and take more time to make a revolution. There aren't any wells capable of pumping at those rates here, so I suspect that it is very difficult to be as effective watering with a 1/2 mile pivot.
Now, the advantage might be that there are way less tires, engines, gearboxes, nozzles, etc. etc. on one 1/2 mile pivot than on 4 1/4 mile pivots.