I think this advice is generally harmful to networking as someone grows, which is vital in today's society
GP mentions "severing" those connections, but I think that's even too strong a phrasing. There wasn't really anything there in the first place, so there wasn't anything to sever. Simply not reading someone else's social media posts anymore, when you didn't really interact with them outside Facebook (or for some people even inside Facebook) isn't really severing anything.
2. Keep the other accounts, just in case.
3. How exactly are remote connections helping? In the Western world, for example, people you haven't interacted with for months and months in real life for sure won't help you financially. For jobs stuff like LinkedIn is probably better, plus regular chats on 1 instant messenger. You don't need Instagram to keep up with them.
If someone's goal is to achieve CEO and/or the top 1%, certainly every single connection could hold extricable value. I'm perfectly fine hovering somewhere in the middle, even knowing I have the capability to achieve much more. My future is uncertain; I probably won't retire when I would have liked. I've accepted that, and choose to live in the present rather than focusing on the future. I know at least I won't die miserable tomorrow.
I don't deny I could have done better financially by maintaining the status quo. Now that I think of it, I'm doing worse financially than when I was using facebook & twitter. I had more money, and my career was progressing at a much higher rate, but I was inconsolable. Without the money, and without the accompanying social media-imposed drag, I see the world more clearly. My relationships are stronger with my wife, kids, and close friends. I am much happier.
With GitHub and Discord, these 3 are really hard to boycott for programmers (even more to publicly shame people for using them). And yet, we must dissent.