Depends on the environment. For example I used to work at a place with 12 electrical engineers who reported to one manager. When I did my project schedules it didn’t matter who worked on the assignment – as long as somebody did. I left the assignment to each project up to the EE manager.
For that resource pool I had 1050% availability (leaving some time for non-project work, etc.).
In my case the manager didn’t need to approve – it was just a matter that the work was coming at his department because the sales department was able to sell the project. I was merely reflecting the estimates which were used to quote the job. (Estimates in that environment were typically based on similar jobs from the past, or sometimes per-job estimates which came from that same EE manager).