I think that the class No Impact should be rename to Low Impact.
Different Change Classes come with different impacts but in the real world there is no change which has zero impact. There is at least some impact from any kind of change because of which I feel that No Impact should be rename to Low impact.
Below are few cases where we are using No Impact change request
1. This change is migration of the databases from SQL Server 2012 to the new SQL Server 2016
Description: There will be a short outage when we move the databases for the duration of the move until we update the connection alias to the new server\instance.
Comments: As per above description there will ab short outage during the migration which will be considered as low impact instead of no impact.
2. Change name of an Application
Description: We have a use case in which we need to change the application to meet business needs.
Comments: Application name change will affect the transnational and functional data and the implementer will have to manually change those so this will be considered as low impact.
There can be similar type of multiple scenarios but I have listed a few. This feature would be pretty and could help in large organisations.