gfxCardStatus is used to manually switch between integrated and discrete graphic cards on the MacBook Pro. My 2011 model had some issues in the past (before fixed by Apple) and I prefer turning off the discrete graphics card if not required. The app does this automatically (f.ex. no external monitor at work).

After using gfxCardStatus for quite some years, the app seemed to stop working after my latest OSX update run. As the latest version 2.3 by CodyKrieger has not been updated for years. However, steveschow updated and optimised it and that version works with OSX High Sierra.