Here's 2 usecases that we need in Lens:

1. When there’s no breakdown but there is a horizontal axis and I want to show the tooltip and allow user to filter by horizontal axis value, but it doesn’t make sense to allow them to select count of records as a serie as we cannot do a filter based on it.
   

2. We have 2 layers, one with breakdown dimension set and the other not. The series from the second layer should not be interactive either because we cannot create any filter here.