Sometimes it is difficult to zero in on the exact drop site when adding a widget to your user interface. For example, when adding a pushButton to a cascadeButton, it is easy to miss the drop site and end up with the pushbutton parented to the wrong widget. In cases like these, it is usually much easier to select the widget on the palette with MB2 and then drop it on the desired parent widget in the Browser. If you prefer the WYSIWYG approach, then the next question on Keep Parent might be a solution.