Capacity planning is working out how much office space you need for the people who actually show up. In a hybrid workplace that is no longer headcount times one desk; it is peak attendance, day-of-week patterns and team clustering.
Get it right and you cut rent without crowding anyone. Get it wrong and you either pay for empty floors or turn Tuesdays into a scramble for desks. Booking data is the most reliable input, because it reflects real behaviour rather than survey answers.