I've had times where being able to instant-message or just send emails made it easier to talk with an old boyfriend or a new acquaintance that I thought was attractive; it would have been clunky to write letters, and too pointed or too immediate to talk on the phone. I don't know if the fact that electronic communication made it easier to talk with someone I thought was attractive was a good thing or a bad thing. The communications never led to trouble, in other words, no affair or "let's meet up" or anything like that ever came from them. So in a way one could say it was a nice way to reach out and have some warm contact with someone that was not the usual person in my life, with no pressure on my real relationships. On the other hand, a stickler would say that if I had put that energy into my relationship (that I expended on the emails), it might have benefited my marriage. (It's awfully easy to build up a fantasy relationship as more fun than one's real relationships.) I think when looking back that it kept me happier and able to face my mundane regular life, and therefore I didn't go out looking for anyone else. But this could just be justification. Someone might argue that my pleasure in the communications was indirectly shutting my husband out.
Another thing I don't like about social media accounts is how they expose you. My sister in law started a family FB group. Oh great. It shows when something is seen and by whom. No more waiting to give an answer on if I can come to yet another family event. LOL They know I know and just haven't answered! I really don't want to be in such close contact on a regular basis with the in laws. But on the plus side, one sister in law that is quite snarky had a negative back and forth with another family member and it made everything awkward so no one has posted there in over a month. LOL Maybe I can quietly exit the group and no one will notice . . .
Both of us have fb and ours is an open book with each other. Our relationship is strong enough where neither of us worry about the other one doing something stupid. Same with our phones...neither of them are locked as we are pretty boring people so for us it is no big deal. I have seen MANY times where relationships go to he!! due to the things you mentioned. There are so many fake people on these sites and many fall for it. I am only friends with people i know. I dont usually take any friendships from friends of friends if i dont know who you are. FB amuses me and that is it!! My momma always said the internet will be one of the greatest things and at the same time it will be the biggest downfall also. She was right(again)