If you, as a freelancer, book times for a cooperation project for which the approval process is active, you can only bill the times after they have been approved. You can submit a 'timesheet' at any time to request approval. You will be informed of the status change by e-mail and can bill your times as soon as the times have been approved.
The approval process can be optionally turned on per user & project. As a project owner you decide which of your team members need to go through the approval process and which not.
If the approval process is turned on for a team member, he/she can only invoices approved times & expenses.
As an organization admin, you will be informed of submitted 'timesheets' via email and can then approve or reject them. Alternatively, you can add someone outside of your organization to the project as an 'Approver'. This could be a customer of yours, for example. The 'approver' is then also informed via email about outstanding 'timesheets' and can then approve or reject them. The 'Approver' only sees the booked times on the 'Timesheets' but no hourly wages.