It would be interesting to hear if the addition of Reddit data makes LLM stronger or weaker.
Outside of some (technical)subs most of the comment seems to be of a far lower quality than what you find in books or in websites.
Someone did a finetune w/ data from 4chan and found improvements on several popular benchmarks, so ... maybe?
For years before LLMs got big a comment I would often see was, "Google search is worthless now. I basically solve all my problems by searching reddit."