A Task Booking is a is a non chargeable operation. It is usually used for e.g. Client Meeting, Company Meetings, Out of Office, Archiving, Administration work,...). It is not linked to a Client or Project.
Tasks share the same Global Statuses as Project Bookings. Creating and modifying Tasks work the same way as for Project Bookings.
Note: there's no extensive Reporting on Task Bookings. So if you need to report on work you should rather choose a Project Booking or Personnel Events that support reports.
To get a quick overview on Task Totals per User, you can use the Long Form > Object Tree.