They're sort of like a walking buffet that you can talk to when you're bored.

They're going to be crucial to our survival in the coming apocalypse but in the modern world they don't serve much purpose.

I wish you weren’t downvoted. I had the same question while reading the article. Especially, what is the difference between an acquaintance, a friend, and a close friend?

People with whom you willingly share your time and interests, and you aren't romantically involved with.

For me friends are people to get drunk with them on weekends. ...so i assume it is very subjective

"Friends" by Robin Dunbar explains that pretty well. Highly recommended.