My best friend is one of the most amazing people I know. I can talk to her about anything, and I know she won't judge me harshly or criticize me in any way. We talk for hours on the phone, even if we just talked the day before! She is shy, but when she's with me, she comes out of her shell a little more. I think that's great to see! We have a blast when she comes over to my house!
I think the benefits to having a best friend outweigh the detriments. A few detriments may be that you don't mix and mingle as much when your best friend is there with you, and that you are a lot more upset if that friend moves away, since you're so close. The benefits, among many, are: you always have someone to talk to and to support you, you don’t have to worry about making a fool out of yourself around them, and you have lots more fun together