I only do it because I'm too lazy to train my Pokemon for 20+ levels. >.< Like, his Gyarados' Waterfall was a 2 or 3HKO on my Zubat, so I would basically have to pray for flinchafusion hax on every turn, which I don't like to do. It's going to be even worse against Byron, whose Pokemon wall all of my attacks, can't be poisoned, have insanely high defenses, and all have attacks that are super-effective against me. And it was unfun the times I tried it without abusing HM slaves, wandering around and spamming A at every encounter for an hour just to beat one gym. <_> I know that's not how you're supposed to do them, but in situations like these, I scrap the honour system as soon as my enjoyment and satisfaction are compromised.
Oh, and the only gyms I really abused HM slaves with were the 1st and 5th, but for the 1st I only used them because I forgot to save recently, which meant another hour of training to get back to where I was, and, well...yeah.