I often need to create a record ID that automatically increments but grouped by a specific field. I currently do it using the Multi-Row Formula tool doing [Field-1:ID]+1 because there is no group by option in the Record ID tool.
Also, sometimes I need to start at 0 but the Multi-Row Formula tool doesn't allow this so I have to use a Formula tool right after to subtract 1.
So adding a group by option to the Record ID tool would allow the user not to use the multi-row formula to do this and to start at any value wanted.