I think it depends on what kind of person you are.
If you're a person that likes conversing about ideas, brainstorming with others, etc, then having author friends to talk shop with will be amazing for you.
If you're a person that doesn't like your thoughts and ideas challenged, or find it tiresome to debate finer points with someone who you think has a crazy point of view, then keeping to yourself would be beneficial to society as a whole. :)
Personally I like to have author friends who are on the same wavelength as I am in terms of communication skills etc. I don't mind when someone points out a fault in my work, even if I think that particular thing isn't a fault. Broadening myself in terms of being a writer includes being shaped (to a degree) by the thoughts and emotions of others.
I don't like friends who are only friends so I'll read their drivel and stoke their ego. Heaven forbid I actually critique it.
