When my friends and I first started playing 3.5 in middle school, we pooled our money for a single player's handbook (they were pricey back then!) and would constantly be passing it around any time anyone needed to do anything, which really slowed down the pace of the game and made it hard to get intimately familiar with the rules.
Eventually someone found a PDF dump of some books, and suddenly not only did we have access to useful stuff like the monster manual and DM guide, but we could search the text super quickly and get familiar with the rules at home, on our own time.
Now that we're adults who can actually afford the books, we don't need the PDFs - but we still benefit from using phone apps for dice rolling and spellbooks, and roll20 for combat.