Regarding your Timesheet notifications information:
- Timesheet - Submitted
- Will send email to all users with timesheet approval right over the resource
- Timesheet - Returned
- Will send email to all users with timesheet approval right over the resource
- Timesheet - Overdue
- When the project manager clicks on the Timesheet Reminder icon, email is triggered to the user to whom the timesheet belong.
- Project - Added Participants
- Will inform the resource they have been added to a project (both as Team and Participant). Any time the resource is added to the team it is added automatically as Participant so this notification could really be for both.
- Project - Removed Participants
- Will inform the resource they have been removed from a project as a participant in Team - Participants only. Removing from the Team Staff does not trigger this
All these notifications are OOTB and things may work differently if you are using a Timesheet Approval process.