Catching up with an old friend can be incredibly grounding.
Grabbing a drink with someone who knew you in younger years can bring back a flood of good memories, help integrate your past and present self, and also solidify a long-standing bond.
Conversely, there are times when running into someone from your past is a horrifying and depressing tale. Maybe their views on the world changed radically, or they didn't change at all which comes with its own depressing results.
I knew a girl in high school who was pretty cool. We went on a class trip and spent a lot of time hanging out, then later I went to a few punk shows with her. 7 or 8 years later, I was back in town visiting.
I stopped at a gas station to fill up, and this emaciated, dirty creature stepped out of the shadows and asked me if I had any spare change. It was her. She looked like she hadn't eaten in days and had track marks all up and down her arms.