Most gyms spend far more on attracting new members than on keeping the ones they have. The number that decides profit is not new sign-ups; it is the renewal rate. A member who renews for two years is worth four who join and drift away.
The first thing that makes renewals happen is knowing whose membership is ending. A paper book will not tell you. A membership system that warns you days ahead creates the chance for a call or a small offer, and that is the difference between a renewal and a loss.
The second is attendance. A member who has not come for two weeks is the one closest to cancelling. When that is visible, you can send a message or offer a session with a coach — and most come back.
Finally, class booking. When members see what is open and book themselves, calls drop, and you learn which classes are genuinely full and which times need changing. Those decisions raise usage without adding a square metre.