Recipe books get left in the office. I've seen it at every bar I've ever worked in or consulted with. Someone puts real effort into a binder, prints it, tabs it by category, and puts it behind the bar. Within two weeks it's in the back office on a shelf next to last year's health inspection and a stack of distributor catalogs nobody asked for.
Spec cards don't have that problem because they live where the work happens.
A spec card is a single sheet for a single cocktail, laminated, and stored on the back bar within arm's reach of the person building drinks. The bartender doesn't have to flip to page 23, scan the index, or remember which binder holds the current menu. They pick up the card.
When a recipe changes, you reprint one card. Not the whole book. One card, five minutes, done. With a binder, updating a single recipe means reprinting the page, finding where the old one is tabbed, removing it, inserting the new one, and hoping nobody made notes on the old version that still matter. The card system makes updating frictionless.
Books also create version control problems. The binder from the spring menu is still behind the bar in October and nobody knows which version of the whiskey sour spec is current. Cards are self-evidently current or outdated. A card with a date on it tells you exactly where it stands.
The card system requires maintenance. But it requires less maintenance than the book, because updating it means reprinting one card instead of rebuilding a document.