Personal preference I'm sure, since some places have more predator access than others and it'd depend on how secure that run is.
The chickens can't defend themselves at all at night, they can't see in the dark, so if they're roosting and something did get in, they'd be unable to get away. At least in the daytime, they can see and would try to get away or make enough ruckus to alert someone.
I keep mine in at night because we have way too much wildlife that comes around that would love a free chicken dinner and I sleep better knowing they are up safe and sound.