It depends on what you are trying to schedule.
A task with a start and end date will book everyone on the task for that time window.
Bookings can have both people or non-people resources involved, and one or more events per resource. Each event can have different start and end times.
For example, on a task to prepare a proposal with a colleague, you can add a start and end date to book you both for an afternoon when you will both work on the task.
However, for recording sessions for a project, you might want to book an engineer and a studio for different slots over a week. In this case you should use a booking.
Of course, you can mix and match for the variety of work that you need to do.