Keyboard shortcuts can be a great time saver when working within GIMP. Rather than navigating through the menu structure to find what you are looking for, if you learn some of the common shortcuts it will increase your productivity greatly.
Using GIMP for Windows you may have noticed that the toolbox is always on top. You maximise your image window and the toolbox stays on top obscuring part of your image. Some may argue that this give you access to the toolbar whenever you need it. Personally I find it annoying.