The one thing that would always be useful is to know medical history of the biological parents--some conditions can be prevented or kept in check with that knowledge, or can be more readily diagnosed if there is a known background.
To be honest, this was the only useful thing that I got from them. My mother contacted the family and members we knew to get medical history. My bio father only lived 10 minutes from my house, my whole life. He made sure to keep himself scarce during the first 18 years of my life. But then I started having medical issues right after High School and unfortunately, I did need some information. Thankfully, he agreed to give info to his sister to give to my mother (to avoid talking to me). Other than that, I was surprised to find out how much I didn't want a drunken coke addict in my life. I didn't miss out on anything. My adopted Dad gave me everything that a little girl could ask for from her Daddy

Curiosity is always great but don't give yourself an opportunity to be let down and disappointed. Sadly, I did that to myself and it hurt so much. Please don't do the same thing to yourself.