When you derive a plan, you copy the details of the existing plan and then amend the plan to add in any custom fees or product specific details. When the plan research is updated by IRESS, any areas of a derived plan that have not been altered will be updated by IRESS. Any area that has been altered will remain the same.
It is recommended to derive a plan where only some of the product features are customised as you will benefit from the automatic IRESS updates.
A custom plan is useful when you want to compare an existing platform against managing direct investments such as with a Self Managed Super Fund (SMSF).