You can book a desk for a guest with the guest's email address. Global admins, owners and custom roles with the delegation permission can reserve a desk for a guest. On the desk panel, enter the guest's email in the Book for... field.
When you add a guest's email as a visitor and book or assign a desk with it, Robin does not make the guest a Robin member. The guest cannot log in, so the guest cannot check in to the desk.
Robin has only the guest's email address. The guest's name does not show on the desk or in people searches.