Checking "EXCLUDE" allows you to exclude a subset of users by selecting Access Definitions and/or providing direct input of specific users, groups and/or certifiers.
In case multiple Actions are to exclude the same users, you can either use (a) corresponding group(s) from the public addressbook in the direct input field, or create so called Access Definitions in the MC Configuration database for further re-use across multiple Actions.
NOTE: When checking EXCLUDE without selecting any Access Definitions and without supplying any direct input, all users who have the role [Admin] in the MC Configuration database will be excluded from the respective Action.