When two project managers/admins share a resource, when that resource submits their timesheet, either of the project managers have the ability to approve the entire timesheet for that resource. Well.. what if one of the project managers does not agree with regards to time spent on his/her project? Then they absolutely have to meet up to review the timesheet together. This is inefficient.
Instead, as part of timesheet submission, the approver should only get to approve projects for resources that they are authorized to approve, as opposed to the entire timesheet submission.