Crooks will look at it to see what they can get out of it. Passwords, email, blackmail material. If nobody benevolent looks at it would we ever know what was actually leaked?

After previous leaks, the data has been looked over to produce lists of compromised accounts which at least one website lets you search to know if your account was in the leak (Kotaku/Gawker leaked my shit years ago). The data can be used to provide stats on the most common passwords.