I am raising barred rocks straight run chicks for precisely that purpose. They are ALL eating me out of house and home, and I'm wavering between thinking most are females (color/feathering patterns) and most are males (gigantic legs/combs starting to color/body mass)... they are 3 weeks and some are obvious, but most aren't. I got straight run because I wanted the full experience of raising and butchering my own birds for the freezer.
That said, my kids are growing literally like weeds and already seem gigantic - they will be dispatched between 12 and 16 or maybe 18 weeks, to experiment with "doneness". They will get plenty of exercise and food, but they are not meat birds and will not eat themselves to death.
I guess it depends what you want. If you want tender meat without an ounce of work once the bird is slaughtered, yeah go ahead and sequester them. If you want "farm birds" that have served their time and are done with it, let them out. The hormones aren't around to toughen the meat before about 18 weeks, so anytime before then you should be totally fine either way.