The "Uncommitted" feature for partitions should only be used by the default Inbound and Outbound classes. These classes are auto-created.
Use the literal uncommitted to indicate that the guaranteed minimum allocation is whatever is not committed to other partitions. Normally uncommitted is used only by the default Inbound and Outbound partitions.
Zero means that you are guaranteeing no bandwidth but you are allowing a traffic flow to acquire bandwidth (burst) if there is available bandwidth outside the class. Uncommitted means that you are using the bandwidth that is not committed to other partitions. It is already present and Inbound and Outbound parent partitions and should not be used again.
Support recommends that you not use Uncommitted partitions for child classes underneath Inbound or Outbound. Use the "0 or greater" burstable option instead of using the Uncommitted option.