I go to /r/fantasy and ask for recommendations. I will probably get someone recommending goddamn Malazan* no matter how applicable it is to what I asked for. I will also get a lot of recs that are just a title, maybe a title and an author, with no further info. Some authors who hang out there will pimp their own books. Maybe someone recommends Name Of The Wind and a mini-flamewar about book 3 taking a decade and counting happens. I end up with a lot of unfiltered recommendations, and an overwhelming amount of research to do on them.
I go to a good bookstore. I can wander into the SF section and find a whole bunch of staff recommendation cards on the shelves next to things they’ve loved. Maybe there’s a list of Hugo and Nebula winners. Maybe some new stuff the average reader hasn’t heard of. Maybe a “if you liked THIS THING then try THIS OTHER THING” card on the shelf points me to something new. I’ve got a fairly small selection of recommendations, curated by people whose job is partially to keep up with new fiction and recommend the great new stuff. And maybe something outside my genre comfort zone catches my eye on the way to the SF/F section...
Also it is TONS easier to get an idea of just how long a book is when you’re picking one up off the shelves. One cover image and maybe a little tiny text note of how big the file is on Amazon’s page is a lot less information about the sheer size of the story I’m considering picking up.
* /r/fantasy loves this turgid-ass sprawling account of someone’s D&D campaign, I finally tried reading the first book and gave up after three chapters, then got told that “everyone knows it doesn’t pick up until book 3” and life is way too short for that IMHO...
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TL;DR: Reddit ain't gonna give you professional recommendations. Reddit will give you a bunch of recommendations of stuff twentysomething guys with a ton of free time on their hands like.
You've mentioned recommendations and exploration but things like Goodreads have similar tools - you can follow users who have similar 'likes' as you, you can read lists by people who have similar tastes, and you can get recommendations from the 'pros'.
I'm sorry I mentioned Reddit. I really did mean any online medium, Goodreads, random book forums, anything else.
With a bookstore, you can reasonably expect, at least to a certain degree, an authority figure. With facebook/reddit, you can reasonably expect nonsense, and maybe one somewhat knowledged guy piping up in a wave of shit.
Tbh, I have no idea why you'd bring up reddit or fb instead of at least hn, where the noise to signal ratio at least attempts to approach something useable.
Reddit and facebook are where you go to accidentally stumble into something useful; not when you're searching for it.
In fact, if you're looking for an expert, you usually go where few people go: because those you would find there probably have good reason to be there; places where its only worth being if you're an expert in the niche