Yes, I'm a big advocate for multiples of spares, but, especially if you work directly with an agency, in my old experience, everything that happens in a studio or a shoot, is reported/shared with the agencies owner, manager, other models, and eventually, with the hair stylist, clothing stylist and make-up styles.
Keep in mind, good models will have both local, regional or/and national agencies.
Also, an enthusiastic model might just get you a higher level exposure and bigger clients, than just shooting local talent.
I liked working with models who were just starting out and wanting head, glamor, three quarter, full length, swimsuit, underthings, automobile, and various location or themed shots.
She got a beautiful new camisole, and wants to show it off in her book, based on a shot in Elle or Biker Tramps, done.
Besides keeping the model and friends happy and wanting more of your work, if you do no run a good "ship", the owners/managers are/were quite picky in whom they let shoot their models, and no allowing a bad photographer/studio have access to their best/prettiest/bullish people, whom are this week's prime earners for that agency.
Often enough, an agency has particular look they want to see their people in and, guess what, they buy your photographs too, if you deliver "The Shot!".
These are my experiences and it's just good business to ensure you get the shots needed and the talent leaves your studio, with a positive attitude about you, your working style, and the shots that are coming down the line (analog, of course).
IMO.