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Using Expressions in both Diagram Box Conditions and in Records Window Columns is recommended because it checks that you actually have Census Events with associated Source Citations. That is what you are doing.
The alternative uses Individual Record Flags and was popular before Diagram Box Condition Expressions were introduced.
Each Record Flag can cause a Census Icon to be displayed on the Diagram Box by setting the correct Conditions.
Since you use Expressions, the Record Flags serve no purpose, so are superfluous, and might as well be deleted to avoid any future confusion.