Faisal,
I won't say if you need or don't need them. But basically the functionality is given to remove or add mitigation. Let me give you a simple example for removal (where it makes sense from my point of view).
Assume we have a request for a user with several risks that require mitigation.
We mitigate all the risks so that we can approve the request:
For one risk we don't have a control so we cannot save the mitigations:
Due to the fact that I don't have a mitigating control for one particular risk I cannot save the mitigations. But as I spent some time and effort in defining all mitigations (Approver, Valid dates, System, Control IDs, etc.) I would like to save all the others. If I cannot remove the line item with the missing control I have to abort and start from scratch.
To avoid that I am really thankful to have Add/Remove functionality.
Hope you understand what I mean. From business and end-user point of view it makes sense to have such functionality.
Regards,
Alessandro