Per-seat billing, add users to bill automatically or make owner manually add seats?

I'm interested in using a per-seat billing model for a project built around teams, but I've never built or really used a per-seat model before. In Stripe's example here: https://stripe.com/docs/billing/subscriptions/per-seat they have the team owner manually choose how many seats they want to subscribe to. Presumably then the team owner could invite that many users to their team.

I'm wondering if that is the normal flow, or is it typically done where you can invite as many people as you want, and as they join the team your seat quantity is raised automatically. So if I invite 10 people I'm being billed for 10 people, without having to go to my billing page and manually raise my seats to 10.

I just want to follow expectations for how businesses are used to doing this.