I had a good run today with one of my friends. I ran the 4+ mile route with him and pretty much spoke the entire time. The pace was slow and I was not feeling any suffering at all. I literally could have kept up that pace for hours. It wasn't the training run I had scheduled for today, but during the run I realized that it didn't really matter about that scheduled workout. What was more important was that I was able to spend an afternoon run with a friend.
I haven't been training with other runners for many years now. I don't know the reason, I just have strange hours that I keep at work so my running is usually while others are still sound asleep or they are sitting down to dinner with their families.
I do think, however, that it is important to take the time to run with friends. You learn a lot about them, and about yourself. When you run alone, you have many thoughts to yourself that you don't voice to anyone but your internal voice. When you run with friends, you can change it up a bit and bounce those thoughts off your friends, and they can do the same.
In the end, I think both runners gain more than good health and that makes the run, no matter the pace, very worth while.