Nowadays, it's more commonly used to represent the sorting of digital information, like browser "tabs" or app "categories," than an actual card index. It visually conveys the message, "I've organized it by topic."

It evokes the analog feel of the pre-digital era, when vast amounts of information in libraries were managed by hand. As a result, it conveys a professional sense of "meticulousness" or "systematic organization," and is sometimes used metaphorically to describe the planning-oriented J types in the MBTI.