Custom fields let your team add the data points you actually track on a fan, then filter and export your contact database by them. Instead of forcing every venue into the same profile shape, you decide what matters, whether that is a seating preference, a donor tier, or a note your box office relies on.
Every ticket, gift, membership, and message already lives on one profile. Custom fields extend that profile with whatever else your team tracks, so the people building a marketing list, the door staff pulling a will-call note, and the finance team running a report are all working from the same record.