Adding those to the long run you can see there is significantly less total weekly miles in the Galloway plan compared to the others. Am I going to need those miles? Why do most other plans recommend so many more miles if they’re NOT needed?
You've already received some great advice. I hope that my long answer helps add to that. I finished many, many races using the Galloway plans and it took me many years before I even began to understand how and why they worked. I followed them and that was enough. But once I began to understand the how and why the plan worked, I began to really grow as a runner and learned how to deal with roadblocks in training.
One thing I've learned in running is that each person has a different methodology for their plan. For instance, a runner who gets all the proscribed long runs in on the Galloway plan will go 14 miles for the longest run two weeks before the half. Since the half is 13.1 miles, then Galloway's plan followed well has you already knowing that you can go the distance or pretty close to it come race day.
So while I am not qualified to explain the methodology behind other plans, I can also say that following Galloway's plans will work. It carried me to successful finishes in the 2011
Disneyland Half, 2012 Disneyland Half, 2012 Wine & Dine Half Marathon, 2015 Star Wars Rebel Challenge (10K and Half Marathon on back to back days), 2016 Star Wars Rebel Challenge, 2017 Star Wars Rebel Challenge, 2017 Star Wars Dark Side Challenge which came just days after I had been working 12 hour days for 2 consecutive weeks on the heels of 10 hour days for 2 consecutive months. I used Galloway principles to craft my own training plan for Avengers 2017 Half Marathon since I had less than optimum time between starting to train and the race itself, and went back to the Galloway plan for the 2018 Star Wars Dark Side Challenge plus the 5K thrown in to boot, which was also ran in similar conditions to the 2017 Dark Side Challenge.
I've listened to him speak a few times at runDisney Expos and heard him interviewed on podcasts as well. He is a former U.S. Olympic team runner so he knows his stuff. I will do my best to explain his ideas.
1. The key to any training plan is the long run. It helps you build up your endurance to the new distance. However too much running, too soon can lead to injury. This is why Galloway generally builds up to the long run by adding 1.5 miles to the previous long run distance. The buildup is gradual enough to get you to the distance without trying to do too much too soon.
2. The ability to build up to the long run distance lies in doing the maintenance runs twice a week. Generally you maintain your previous long run fitness level for 2-3 weeks without increasing distance. If memory serves, the Galloway plan usually has 2 maintenance runs of 30-45 minutes on Tuesday/Thursday and a long run of x number of miles on Saturday. Near the end of the plan, I think you would do 12.5 miles 4 weeks before the race, 4 miles (if I'm remembering correctly) 3 weeks before the race, and 14 miles 2 weeks before the race. Doing the 2 30-45 minute runs during the week and the weekend run will help you maintain the fitness necessary to build up to the race distance.
If a runner trains too much, then that will negatively impact their performance on race day. A runner may head into a race with an overuse injury and may turn a small injury into a much bigger one. This is why race plans have a taper period where the number of miles being ran tends to drop quite a bit during the last 2-3 weeks before a race. This does not hurt race performance because it allows the body to heal, rest, recover, and be hopefully fully healthy on race day itself.
I believe that Galloway seeks to reduce overuse injury by keeping miles low and allowing for days off between runs.
I hope this has helped you. Before my very first race ever at Disneyland, I just wanted to finish. That was all I cared about. I chose the Galloway plan because he was a former U.S. Olympian who had completed hundreds of races and guided many runners to successfully completing their races following his methodology. It also helped that the plan was free as opposed to buying a book telling me how to do it and it offered a path that I could comprehend.
Well, I followed that first plan very imperfectly. I slacked off early in training, skipped a few runs, skipped even more weekend long runs, and about 3 months before the race, realized I had better start taking this seriously. I had to modify the plan and cut out all the short weekend runs in order to get all the weekend long runs capping at 14 miles 2 weeks before the race. I had no idea what I was doing and was truly terrified that I would not finish. Well I got through all of those long runs, even the 14 mile one. And I still didn't believe I would do it.
Race day came and I allowed my fears of failure get the best of me. I started the race much too fast and less than half a mile in I felt like I had shin splints. I knew I could not go another a few feet in this kind of pain, let 13 miles so I slowed down to an acceptable pace that I could handle. I decided I would go at the acceptable pace until I either finished the race or got swept. If I was going to fail, I would fail on my terms. I would fail because I was not good enough as opposed to didn't even try.
So I just kept putting one foot in front of the other. Slowly, but surely the mile markers kept showing higher numbers. Still nobody warning me that I was about to be swept. And like many others before me, I eventually crossed that finish line. The Galloway plan really does work. Just put in the time and effort necessary and above all else, trust your training.
The day after my first half marathon, I saw other runners who had completed the Goofy challenge that year at Disney World. I could not fathom how in the world they ran a marathon the day after running a half given how exhausted and sore I still felt. I literally believed that doing the marathon was impossible for me. Yet this year, I successfully finished the Dopey Challenge as part of my first marathon.
In the years since that day, I have accomplished many "impossible" things as a runner. Or rather I have accomplished many things that I once believed were completely impossible on that day. And they all started with following the Galloway plan. It works.