yes, it's easy to connect with all my old friends.
we can have a long list of friends and also find old friends with whom we were not in contact, yes.
yes, because they are a faster, easy, and affordable way of communication.
yes. sometimes we can't talk via phone calls due to privacy issues. so, we can use messenger applications wisely, and moreover, we can't send images, videos, documents, location, etc., via phone calls.
yeah
yes. facebook keeps people connected even if they live very far apart.
i regularly use facebook and whatsapp. these are cheaper compared to phone calls. if we talk about letters, it will take too long to reach and get a reply back. so whatsapp does well. but letter writing skills are being demolished.