Despite the authority given to a project manager, it's still very much a job that involves hard work. The project managers is oftentimes involved in hiring the staff needed for project completion. She may be able to choose them out of employees already on hand, or she may start from scratch in her involvement. These are people that she'll need to trust to complete the task well and with speed. They are also people she needs to be able to have a good working relationship with in order for all workers to give their all to a project. It's a challenging task.
Besides working with project workers, a project manager must set up, attend and run meetings on a regular basis. She also will vet vendors and decide who can further help the project along. She'll assign tasks among those working on the project, and sometimes she'll have to switch tasks among workers. While this can lead to friction, a project manager must finesse the situation so that all sides feel as though they achieve a win-win.
People skills are a necessity for any project manager.