A standard task code is used for a task used within numerous routings. As an example a cutting operation may always use the same tools, personnel, description and quality measures. Then when you are creating a routing there is a standard task code option where you can assing all of these attributes to the operation in one go by picking the standard task rather than the description coming from the work centre and you having to define the tools etc against the routing.
With litle customization you can extend the use of standard tasks. We added fields Setup time, Run Time, Work/Machine center No. etc., in which we can write deafult values. Thus you can more easily build routings without having to know exact Setup and Run times for eacht routing line.
The standard Navision table has very limited functionality, in my opinion.