My rule: online connection needs to foster offline connection. So if my kids want to borrow my phone to FaceTime their grandma, I say yes! If my daughter wants to look up a craft idea together for a gift. Sure! If they want to dance to The Trolls soundtrack with their friends? Just hit play.
As for other screens, we usually find plenty to do otherwise, so we save TV And movies for sick days or really special occasions. :)