In the early 2000s, a "meme" about Dunbar's Number was all the rage, helped along by Malcolm Gladwell's book, "The Tipping Point." The science of it is as complex as the whole "10,000 hours to becoming an expert" thing is. But it's been helpful to me, particularly when thinking about limitations of time on what I can do.
Short Story: Dunbar was an anthropologist at the University College of London who, based in some part on evolution ideas, predicted that 147.8 was the 'mean group size' for humans, which matched census data on villages and tribe sizes in many cultures. (from LifeWithAlacrity.com, see whole article here).
I know, you heard evolution, but don't throw the baby out with the bathwater, as my mother used to say.
Dunbar's Number has been in a ton of books and also in a ton of studies. I'm not an evolutionist, but there's been plenty of studies to show that the number is about the average. Bigger groups via technology don't disprove the theory: they are audiences, not communities.
However, it takes a lot of time and work to get to a community of 150 - the research suggests half the time you spend with a group has to be spent in "social grooming" (which some theorize is, for us, social communication). Most groups are far smaller than that. That LifeWithAlacrity article above looks at Dunbar's Number in relation to online multiplayer groups and sees the vast majority of groups have sizes around the 30s, 60s, 80s, 100s, and 130s.
Dunbar's Function from LessWrong builds on LifeWithAlacrity, together they look like:
Shorter: Peak is about 7 for simple groups, and about 60 for complex groups, and every community fractures in some way by the time it approaches 150.
Technology does not change this. Partly, it's an aspect of the capacity of your brain to remember/recognize people (which tech can help with). Partly, in my book, it's just this: you only have so many hours in the day. You can't spend them with everyone. The more hours you spend with one person, the less with another. So if you've a tribe of 150, and you spend an hour with each, that's a month's work.
So, how do we apply this to our own work? Everyone needs a group of people they're working with (mostly). How many people you choose determines how you spend your time.