According to Francis Bacon's "Of friendship" describe the three fruits of friendship.

One of the first fruits he describes as follows:

A principal fruit of friendship, is the ease and discharge of the fulness and swellings of the heart, which passions of all kinds do cause and induce.

With the understanding of the view of the human body at the time, that it was full of humors that sometimes needed to get out in order to be healthy, one of the main benefits of having friends was that you could get out the "fulness and swellings of the heart" so that the body would remain healthy.  Obviously you can talk and share with a friend, and at the time this was seen as connected to bodily health as well as spiritual.

The second he describes thusly:

For friendship maketh indeed a fair day in the affections, from storm and tempests; but it maketh daylight in the understanding, out of darkness, and confusion of thoughts.

The idea that a friend can help you to understand the thoughts that rattle around in your head is another that Bacon points out as one of the principal benefits.

The third I will leave to you to find.