My ex used to prefer not to band, but he said they had to be away by early September or they stopped growing and became "woody", as the hormones took over and they became more interested in sex.
Then we had a couple of years with movement restrictions and decided to band everything so we didn't have to be sending entires off when it was suboptimal, and or be stuck with them into the autumn. He continued to get top grades, but we did maybe need to manage food intake a little more closely to stop the greedier, lazier wethers getting too fat. As we supplied Morrisons, who prefer grass-fed or as close to it as possible, feeding less and keeping them on a week or two longer worked fine for them. Prices of course fall from July onwards, so we might sometimes get 15p or even 50p per kilo less for that two week deferment. Most years we felt that the savings on cake pretty much equated to any reduction in ppk. And we appreciated not having the stress of making sure all the entires were away by September, even if they would have benefitted from another month.
Plus, weaning also gives them a check, so with all boys ringed we could send everyone off their mothers and no-one had to have a weaning check.