I began doing it for a couple of reasons. I hope listing them doesn't make me look like a conspiracy theorist or a cynic, because I'm neither!
First I really don't like not being able to identify on sight what's in the food, and the absence of a list of ingredients that are clearly foodstuffs rather than additives worries me. I understand why it is that way, but I don't want to buy into things done for the convenience of manufacturers needing to meet regulatory standards, instead of for my convenience, as the customer they are both supposed to be serving. Connected to that, things that are not naturally food can also look, on lab analysis, like food, so could go into feed and pass regulatory muster, but still not be something I want my chickens to eat (melamine to boost the protein in baby milk is a famous recent example). Which raises the spectre of food fraud, which exists in the human food chain (horse meat sold as beef for example) so is almost certainly present in the animal food chain; and there can be few places easier to hide it than a homogenized pellet for an animal with a relatively very short life (which takes us back to 1).
Long supply chains and globalization both offer serious impediments to anyone along the chain knowing where something has come from and what it is going into, and an excuse for anyone along the way to shrug their shoulders and claim ignorance. Again you see that with the human food chain, which has higher standards than animal feed. So I prefer to buy locally grown recognizable foodstuffs for me and mine. I don't think it's more expensive and it may even be cheaper. It's certainly fresher.
I ferment because I think it helps a lot with whole grain feed; it reduces the anti-nutritional factors that seeds have built in and that a lot of the industrial processing also aims to overcome; it also adds some nutritional goodies, softens the grains, reduces waste to zero, and more; if you're interested have a look at the article Jenjens linked to
https://www.backyardchickens.com/th...-me-research-study-on-fermented-feed.1428955/ or other papers and webpages - there's lots out there.
I raise the mealworms. I bought the first tub from a fish supplies shop early 2020 and we're still going strong on that same £2.50 investment! Story here
https://www.backyardchickens.com/threads/first-attempt-at-mealworm-farming.1350136/
They eat 1 sack of bran a year, which is going up in price but still a tiny fraction of the cost of a year's supply of dried mealworms. They get the bits of vegetables we don't want to eat, so I count that as free. And, bringing the story full circle, I know exactly what my mealworms have eaten! (Live mealworms are also permitted under current UK legislation, unlike dried.)