Do you want the public or large numbers of semi-public users (e.g. students) to be able to book resources without creating or buying a separate user ID for each? Do you have many internal users that just need to book resources occasionally?
With the Extended option you can have an unlimited number of ‘Reserve’ users without purchasing ID’s for each user. These users that can book specified resources, optionally subject to administrator confirmation. Your ‘Reserve’ users can only use one status when making a booking. These bookings show up with a different color so administrators can see them at a glance and confirm, change or delete them.
You can add ‘reserve’ user ID’s in bulk, or allow them to create their own ID’s from their email address. You can limit those addresses to those of specified domains.