Viewing rights are user dependent:
Admins - see everybody's remaining hours, availability, and bookings
Project managers - see the remaining hours, availability, and bookings of the whole project team for the project they've been assigned to as a project manager.
If they're not assigned as a project manager to a project, they will still be able to see the remaining hours and availability (without bookings) for the users who're part of their projects.
Regular users - only see their own remaining hours, availability, and bookings. They can't add bookings for themselves if they're not project managers.