Impact Assessments enable you to identify options for an Initiative - what changes are being considered. These options can then be compared against each other to understand the differences. What impact on Benefits and Measures is one option expected to cause rather than another? The best option can then be chosen.
Before, all Benefits in a Workspace were included in an Impact Assessment. This was sometimes a lot!
New is a setting that filters out Benefits of no interest to the selected Initiative, reducing the Benefits and Measures included to a more manageable set (when you have a significant number of Benefits!).
Use the cog on the Impact Assessment screen to see the new setting.