Sometimes it is needed open more than one project and several files from each open project. If needed continue working with one project then others must be closed. But open files from these projects remain open and they are exist in open files list. It is long and not useful. To close all files from already closed project it is needed navigate to each file name and check if it's path relates to not open project. Then click close button on each file name. This is very annoying and time wasting operation. Therefore I suggest add action
Close project <Name> and all it's open files
to menu File in QtCreator and similar action to project's submenu (right button click on project name). This action acting will be very simple and completely described by it's name.