After Google bought Deja and turned it into Google Groups, they spent quite a lot of effort reconstructing old bits of Usenet, such that the archives now go back to 1981. When they announced this, I wondered why they’d go to such an effort. I thought that perhaps it was just that there were some Google engineers who were historians.
But now it’s clear that there’s another good reason – whether they thought of it originally or not. Prior art for patent lawsuits.