Well, you will have less opportunities for social activities. So you are missing out on social activities. These became increasingly stressful with age, so I'm not really missing them. There's many solitary activities you can fill your life with. Even solitary travelling, if you don't have the need to be in a familiar environment all the time.
I believe generally it's best to make sure to have at least 1-2 good friends. It could have beneficial effects on your mental health. Though I'm not sure. Still trying to figure it out after not having (online) contact to friends for over a year.
Having offline friends wouldn't be of any use in my case, as I don't want to meet them or participate in any social activity. I also don't want anyone to visit me. So I didn't see them for over 10 years. And my mental health actually got better in the past 10 years. E.g. I'm much less stressed and depression (other than the dysthymia) occurs only rarely. Though the reason for that may be that I stopped working over 10 years ago, so I'm not forced to interact with people anymore.
Though I wouldn't recommend to become a hermit like me Humans are "social animals". You too have a "social animal" part in your brain. It's probably best to keep the "visiting friends" activity as a part of your weekly or monthly routine.
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Asperger syndrome (diagnosed), schizoid personality disorder (self-diagnosed), dysthymia (diagnosed)