1. A method for managing mainframe computer system usage comprising: establishing a first group definition, the first group definition including first and second logical partitions executed by the mainframe computer system; establishing a first group policy, the first group policy including first and second partition processing capacity limits, and a time criticality level for each of a plurality of workload tasks assigned to the first and second logical partitions, each time criticality level indicating whether the workload task associated therewith is time critical or not time critical; monitoring performance of the first and second logical partitions in executing the plurality of workload tasks; determining, based on the performance monitoring and the first group policy, if either of the first and second logical partitions has a capacity deficit or a capacity surplus; and if one of the first and second logical partitions is determined to have a capacity deficit while the other is determined to have a capacity surplus, automatically balancing the first and second partition processing capacity limits.