Why do they take screenshots of conversations?

Now sure if this has ever been noted, but I've seen tons of articles about pedos where they also have screenshots of their conversations. Why do that? Could this be MSM verified proof of pedos keeping blackmail on each other?

< Following the raid, the department obtained a search warrant for Meek's iCloud account on November 14. They contained backups of two of his devices and included a screenshot of one of the explicit discussions.

Sauce: https://www.zerohedge.com/political/ex-abc-senior-producer-who-rolling-stone-covered-indicted-child-porn-charges