RPGs are my big hobby. I am interested in a ton of stuff and give myself a monthly RPG budget that has gone up with some professional advancements. I buy almost exclusively PDFs now. For the past decade most physical books I have gotten have been gifts.
I was fine running 3e games off of the SRD. I have played many RPGs where I did not own the books at the time or ever fully figure out the rules (Warhammer FRP, Star Frontiers, GURPS, Shadowrun, Vampire the Masquerade, Rolemaster, etc.) I don't need any products to play my hobby.
However I like RPG books, settings and monsters in particular. I want a lot of them. I use a lot of rulebooks and sourcebooks and modules in my games.
I have tons of stuff now in print and PDF. More than I will ever play. More than I will ever read.
Lots of my RPG books I think of as reference material, there if I have a use for them as things come up. When my last campaign as a player wound down and I was asked to take over as DM I threw together a list of 20 adventure path campaign things I owned that I thought would be fun, each with different themes. The group coalesced fairly hard around the Iron Gods adventure path concept and off I went with conversion materials to run it in 5e D&D, and then looking up Post-Apocalyptic and Sci-Fi RPG stuff I had to go with the themes of the campaign. When two players came up with werewolf and werebear concepts for their characters I pulled out my Werewolf the Apocalypse material and we dove into those concepts in my 5e game.
I keep buying PDFs and bundles from Bundle of Holding and Humble Bundle and Itch Io. Even though I have more than I will ever read, there are more I am still interested in having. I expect more to be produced that I will have an interest in as well.
It is good to be in a position where even though I have broad interests in lots of stuff, nothing is a must have, it is all in the would be nice to have type of category.