The most recent update to WooCommerce Appointments plugin (2.2.7) expands capacity management to staff level. This means that your staff can now have a limited capacity control outside product / service level. For instance, if your product capacity allows 10 appointments per slot and your staff capacity is set to 1, staff will only be allowed 1 appointment per slot, regardless of your product capacity settings.
Staff Capacity Management
Capacity on product / service level gives you option to set the maximum number of appointments per slot allowed at any given time for any product assigned. It overrides product capacity, but can be adjusted with staff availability rules for further refinement.