In my opinion, it's a matter of degree.
Social media can be of great service, as per your example of watching your nieces and nephews. People share parts of their lives and interested parties take it in. That's great.
On the other hand, there are people who post the most mundane parts of everyday living for no apparent reason. "Heading into Stop & Shop to do the weekly shopping." "Wow, it was cold this morning." "This woman in front of me was driving so slow this morning, Ugh..."
And then there are the people who really have few original thoughts and little to say -- so they post "made for social media" snippets, "funny" quotes, etc, just to have a presence.
I have decided to eschew social media. Admittedly, I have some accounts with fake names that I use for "research" before meeting with clients. My experience from using those accounts show me that many people waste a lot of time posting what I consider to be stupid stuff.