Picture this.... you've spent a half hour building and testing a query, and you want to add one more field to it... you can't recall its exact name and the auto-complete, while great, does not always get you there. So you type a few chars of of the object name in the left sidebar, click to expand the list of fields... and casually click on a field there while perusing the list and.... your actual query is gone forever, replaced by a single SELECT statement for that one field you just clicked on. Undo will not bring it back.