As an example, I wanted to do some research on early language features of Python (e.g. around 1993). The info is in Usenet postings of that time, surely present in Google Groups years ago. Now, I can't find anything useful. A advanced search using dates doesn't return anything. Their user interface is horribly bad compared to what it used to be.
Another example: I did some research on Deep Blue and Deep Thought, after reading Crazy Bird's book. With the old Google Groups, I could follow the discussion of the Deep Blue tournament, in chronological order. There was all sorts of interesting things like computer chess programmers speculating on how Deep Blue worked and people posting analysis of chess positions. All that is now gone or at least not searchable.
So sad that all of this knowledge has apparently disappeared. There was loads of information shared on Usenet and the storage space required to preserve it would be trivial.