The impact is a measure of the business criticality of an Incident or a Problem. The impact is often measured by the number of people or systems affected. By default, you have four Impact details listed in the list view.
To add a new Impact,
Go to Setup
>> Customization >> HelpDesk.
Under Impact, click New Impact. This opens the New Impact details page.
Provide the Name and Description of the impact.
Click Save.