I do tend to but stuff that I hope to play. The regrets, if any, tend to set in later.
I once bought a slew of OD&D adventures just to sell them all off again a few months later. I kick myself now, but it was what I needed to do at that time.
Other than that, I like to do a little research for an overview of the game rules, but first I'll look at a character sheet first so I have something to reference in my mind while I look at stuff like character creation and combat resolution, though I could have been better at reading stuff like time/movement, magic casting, et cet. RPGs are expensive to buy a bunch of core books and settings just to realize that it's not something I'd really enjoy. It's generally how I got some familiarity with OD&D-AD&D-B/X-RC, which is what switched me to the OSR when 5e failed to deliver my ideas of the modularity that I was hoping for (of course their not mind readers, but given what already existed there were clear steps backwards).
Something like Traveller is different. I don't mind buying a bunch of those books, I can dust them off when the right opportunity comes along, and same for any other old-school games in general. Thankfully, the price point of my wish list demanded holding back just long enough to see Mongoose Publishing standing where I don't want to be, so it looks like I will be buying T5 at some point after all. I wonder where all of those complaints about the complexity and bloat of Marc's newest system came from? The game community around a system was never something I worried about for several years, but I was an entirely different person back then.
I don't mind grimdark settings and rules, but even if FATAL is a really playable system, I'd probably avoid having it just for the shock value. I don't care if other people want it, but that's up to them. I'd really need a good reason to have that to mine some ideas for a toned down version where the dial still sits at 11. The gore and banal (statue) nudity being removed from the Diablo 2 remaster is a good case of going too far the opposite way in a world invaded by man-eating demons.
Edit:
Nope, it definitely has bad editing.