Indicates that the execution to obtain the data for the insight should be an 'execution by reference'.
Execution by reference means that the ExecuteInsight will ask analytical backend to compute results for an insight which is stored on the backend by specifying link to the insight, additional filters and description how to organize the data.
Otherwise, a freeform execution is done, in which the InsightView will send to backend the full execution definition of what to compute.
This distinction is in place because some backends MAY want to prohibit users from doing freeform executions and only allow computing data for set of insights created by admins.
Note: the need for execute by reference is rare. You will typically be notified by the solution admin to use this mode.