For their one here it's just the ability to rapidly comment/uncomment conditions in a query editor while exploring the data or debugging the query, and not having to worry about the leading AND or OR.

I've also seen it in code with iterative adds, for example:

  for crit in criteria:
      sql += " AND " + crit

No needed to add a sentinel or other logic to skip the first AND. I saw it a lot before people got used to " AND ".join(criteria).