I'm not the only one called Peter in this community, but here is my feedback in case it proves to be helpful. if any other Peter wants to fall in, feel free.
Enabling Strict Exclusion will block access to a specific document for anyone who causes the data reduction to eliminate all data from the data model. For example, a user that has a Link field value in Section Access that is not available in the corresponding Section Application table, will cause all data to be reduced awxay. The result is an "Access denied" message.
This situation is often caused by some subtle error in the Section Access code. For example, forgetting to convert the Link field values to uppercase will produce no associations as the SA Link Field values are implicitly converted to upper case by the QlikView engine. The same applies to Link field names.
You can easily check whether SA is functioning as expected by commenting out the Section Access; statement in your script and reloading the document. Put the visible NTNAME field on a sheet, select an arbitrary user and observe which fields, dimensions and objects produce values. All accounts that fail to produce data (or all data stays greyed) will fail to get access if you enable Strict Exclusion.
See also HIC's must-read article: A Primer on Section Access