Activity Types allow you to capture specific activities you want to report on. Examples are
You can select Activity Types when entering time and expense transactions.
For Payroll Reporting, you can specify a Payroll Code for this Activity.
Use the Financial Account for fixed amount entered in the Timesheet (similar to Per Diem) - example bonus for overtime.
For Resource Pricing, you can specify an Overhead Percent value.
You can overwrite the Project Utilization Category.