The gamefowl within the pen will tear themselves to pieces trying to get to the bird on the outside. Not all will do it but the good ones will. They may be just fine 364 days but that one day it's a problem and you have a mangled bird that is useless and taking up your time doctoring him up.
Put it this way. If you can have full grown gamecocks penned and full grown roosters running around close to the pens without a problem your gamefowl are useless.
I had guineas for awhile. After a couple years I only had a breeding pair left. The male was fine then one day he started messing with the penned birds. One of them doesn't have any spurs left. It's not worth the aggrivation.