Menu items that allow you to set a filter before any execution is done will bring a dialogue to the user. This dialogue blocks the user in the ability to view part of the form that is being displayed. This might be annoying, for instance if values are being displayed that the user wants to use in the query.
By clicking, and holding the mouse button, on a part outside of the dialogue you are able to temporarily hide the dialogue and thus able to ‘peek’ behind it. This allows you to quickly look up any value you might want to use on your filter, for example.
I have opened a menu item that shows a dialogue, partly blocking my view to the information displayed in the form behind.
Here, I am clicking and holding outside of the dialogue allowing me to ‘peek’ what’s behind the dialogue.