Comment by Ariarule
I won't bother defending Google-style personalization as it exists for their search results, but since collisions in terminology across fields are common, it's not that hard to see how actual, thoughtful personalization could be useful. Someone searching for "Kafka" is going to want very different results based on whether they're thinking of software or literature. Opinions may also differ over the usefulness of sources, even for people ultimately interested primarily in facts; I find Kagi-style personalization (make your own domain list) very useful, but across Kagi's userbase Reddit is simultaneously one of the most lowered, most raised, and most pinned domains: https://kagi.com/stats?stat=leaderboard
Anecdotally I find myself appending 'reddit' to search terms very frequently. It's effectively shorthand for "I want to read about peoples direct experience with this thing", and reddit is huge and well crawled by search engines. It's astroturfed to hell especially around political topics, but I feel like it's easy to tell when discussions about random products are authentic.