Your phrasing of the last sentence caught my interest. Is the other reason fresh chicken meat, or is there another benefit to keeping them that I can't think of?
Chickens are incredible composters. Put in your raked leaves, almost 100% of your food waste, paper towels if they don't have chemicals in them, grass clippings, etc. They'll be clawed through and pooped on and turned into fresh soil. If you have the space for the chickens, they can be worth it for this reason alone. They're less work than bagging up your leaves and you'll reduce the food volume in your trash to almost zero.
This. How do you harvest/refresh the compost though? Just move the cage over? Do you kind of suspend the cage a bit and let the little stuff fall through?
For me we have a coop and then a fenced in run which is relatively large. I built my gate so I can fit a wheelbarrow inside. I just shovel some out and smooth out the pits I've made. The ground doesn't need to be perfect because the chickens will always be making more compost and shuffling it around. If you had a smaller setup, I'd think a mobile coop & mobile run would serve you really well.
Laying chickens are very different from broiler (eating) chickens. You can eat laying chickens but the meat is much stringier. You can stew them though, coq au vin is a French dish more or less made for these types, even though its the norm these days to use regular eating chickens when making it.
As others have already said, the reason is mainly to cycle yard and food waste, as well as some garden tasks (they can be used to prepare beds as well as cut my lawn). I also plan to raise black soldier fly eventually.