Capping class numbers is partly a safety matter here. Pad and partner work needs an even count and a clear view of who is in the room tonight — that doesn't get sorted out in the doorway.
The money side is the part nobody sees. Direct debits, injury freezes and notice periods handled automatically give back several hours each month and head off the awkward conversation that follows noticing late.
Beginner courses run as cohorts, and cohorts need managing. A six-week intake with a fixed start, a cap and a waiting list behind it fills far more reliably than an open invitation to turn up on Tuesday.