A hen roosting in a nest box is like an Armor Canned Ham, she is a sitting duck so to speak, just waiting on something that's hungry and has sharp teeth to come along and drag her out.
At least if all your poultry roosts on the roost poles there is a better chance that a night time incursion will raise a general alarm and that might allow the hens' keeper to intervene in a timely manner.
Old dried chicken you know what in a nest box is also a nifty place for Chicken Mites to hide under during the day. If the girls roost in the nest boxes that means that you have got to stick your hand in there to get either the *&$% or the eggs out. Each to his own I always say, but I much prefer to shovel poo than to handle poo with my hands.
Finally you must decide if you prefer your morning eggs with or without a side order of chicken poo. If you said the latter then don't allow your hens to roost in the nest boxes.
