I work entirely with PDFs and software (Libre Office, GURPS Character Assistant) when generating characters, devising games that I intend to run, and doing game preparation. I’ve operated that way for several years.
I used to use commercially printed books in-session, as a player and GM, but since the pandemic moved all play on-line, physical books are an inconvenience, so everything is done on the same laptop as I’m using for play.
Edit: I also have a tablet with gaming PDFs on it, for access in-session to stuff that I don’t have as physical books, and the same set of PDFs on my 'phone, in case I want to look something up while out of the house.
While I have quite a decent laser printer, I’ve never printed out lots of gaming material, because it’s never seemed useful. I adapted to using PDFs for long technical reference books at work in the early 2000s, and gaming went along with that. A powerful search tool for PDFs is very useful for gaming; I use Agent Ransack, which works rather well.

