We are social beings and it is vital for our survival and long healthy life to have few good friends; they help us emotionally in times of distress; they give motivation, and you can do things together, plan together, which helps in greater performance in life or in job.
I have also read lot of researches about the importance of friendships in one's life. People without friends, or people who do not meet other people regularly, who spend most of the time alone, are at higher risks of developing several physical and mental illnesses.