Also IMO it's a lesson I give for free to my contacts because I explain why I do not use such services.
Yes, I have occasionally missed out on things as I don't use Facebook, WhatsApp, etc.
However...
I find that instant messaging enables and promotes poor organisational skills in colleagues. Rather than processing tasks in a timely and professional manner, they have a safety net of being able to send a group message at 23:30 the night before a meeting the next day. I also find that instead of a well planned, concise email, these people will spam colleagues with a string of brain-fart messages until, 60 minutes later, a consensus is reached.
Funnily enough, when there is no option for this, people never have a problem contacting me in a professional way.
also rules out usecases for people who aren't actually "settled" and have to follow social norms in some areas- actually expecting a girl to contact me via phone or email before the first date, i'd be living in a fantasy land. it just won't happen