I know you didn't ask me Jem, but I'll give you my views too, lol...
1: I have dual purpose birds, cockerels don't reach good weight for eating until after their hormones surge, so can keep them long enough to be worth putting in freezer camp.
2: Most who have success with bachelor pens say that having them separated from the pullets and hens lessens their reaction to hormone surges and fighting is minimal, but there's usually an exception to that but not as prolific in a mixed sex pen.
3: For breeding you really need to grow out several boys to show all their traits cuz a lot doesn't show til after they mature. You want to keep the best and not end up culling to early.
Those are my benefits, others may be different tho...