One way to access or activate some display- and window-related features in OS X is to use screen hot corners, which you can set up to activate the desired feature by moving your mouse to the respective corner. For example, if you wish to manually activate the screensaver, then you can bind this to a hot corner and then move your mouse there to always activate the screensaver.
Hot corner features can be set up in the Desktop & Screen Saver system preferences by clicking the "Hot Corners..." button at the bottom of the Screen Saver tab, and include options to start or disable the screensaver, invoke various Mission Control and Expose views, show Launchpad, and put the display to sleep.
Some of these options like those for handling the screensaver are only activated as long as the mouse cursor stays in the specified corner; however, others like Launchpad and Mission Control are activated at the corner but remain so even after moving your mouse from the corner, allowing you to interact with the view mode being presented.
While convenient if you need to access these features, having them bound to the hot corners (especially the ones at the top of the screen near the menu bar) means you might inadvertently activate them and invoke a Mission Control view that you might not want at the present moment. This can be a bit distracting and cause you to click a window you do not want and disrupt your workflow.
If this happens, then you can get out of the inadvertently toggled view in several ways. The first is to click an area of the view's background and it will disappear, but requires you do so without clicking an undesired window and bringing it to the forefront. A second option is to tap the Escape key on your keyboard, and the view should be returned, which perhaps is a more preferable option but does require you access this key.
A last option for reverting an inadvertently toggled hot corner is to simply move your mouse to that corner again. The hot corner acts as a toggle for its bound action, so while you can activate the hot corner by moving your mouse there, you an also deactivate it by again moving your mouse to that corner.
Thanks to MacFixIt reader Simon for writing in about this tip.