There are probably as many ways of doing a thing as there are people doing said thing. Most of my batches that are under ~1.080 wind up with 10 1/2 to 11 1/2 gallons post boil, and I haven't seen any drop in efficiency from the smaller batches of the same recipes I did before. I do brew bag in a cooler & batch sparge, no pumps, all gravity flow. I picked up a 15 gallon kettle about a year and a half ago, thinking I'd only use it for the occasional monster beer, but at some point I realized that I never wind up with too much of any particular beer, and usually less than I'd like. Consequently my batch sizes have crept up to where I am now, which is right at the limit of what I can physically handle, and with 12 plus gallons in the kettle preboil, about as much as I can go and retain a safe amount of freeboard for adding hops. The physical limit part is that since I don't pump I have to climb up on the counter and lift the kettle a couple feet up onto a stand so I can drain it into the chiller bucket. Lifting 11 1/2 gallons of 200* liquid sloshing around in a 15 G kettle is as much risk and strain as I'm willing to take. I brew indoors on a gas cooktop, I've found that with the larger batch size on an 18,000 BTU burner de-rated for our 5,000 ft elevation, I need to leave the lid about 3/4 of the way on the kettle if I want to maintain a good rolling boil, with the lid off all the burner can muster is a very low boil that's close to a simmer. That inexpensive Brewer's Edge kettle is one of the best brewing purchases I've made, my pricy 10 gallon Blichmann hasn't been out of it's box in the closet in close to a year.