Resource cost set up

When we do set up of a resource there is a box under costing  as 'standard rate', pls refer attached picture.

Please refer below explanation in the user guide,

If the resource is costed, indicate whether to charge jobs
and repetitive schedules based on a standard rate you define.

Or, disable Standard Rate to enter a rate to charge the
resource in Work in Process for an internal resource, or derive the rate from
the purchase order for an outside processing resource. For outside processing
resources, if you charge a job or repetitive schedule at the standard rate, a
purchase price variance is computed and posted to the rate variance account. If