Developer Options

Developer options gives you access to settings like:
• USB debugging: This is what allows your phone to communicate over the USB port on your computer via the Android Debug Bridge (ADB).
• Revoke USB debugging authorizations
• Take bug report: Grabs the current log files on your device
• Desktop backup password: This option forces a password on those backups, and they can't be restored without that password.
• Stay awake: Force the screen to stay awake while your phone is connected to a wall charger or your computer's USB port.
• Select runtime
• Enable Bluetooth HCI snoop log
• Process stats: Everything you ever needed to know about the running processes on your phone.
• Power menu bug reports: Puts an option in the menu you see when you press and hold the power key to collect and send a bug report (as seen above).
• Allow mock locations: This setting will let you manually write location information, making your phone think it is somewhere it really isn't.
• Select debug app: This setting lets you choose an application to debug. You don't really need to attach it to a debugger, but if you do it prevents error messages when paused on a breakpoint.
• Wait for debugger: This setting is greyed out unless you've set an app to debug. When set up and selected, it simply prevents the chosen application from starting until the debugger is attached.
• Verify apps over USB: Lets Google scan applications you installed via ADB for malicious behavior.
• Show touches: Select this to see a visual cue on the screen when and where a touch was registered.
• Pointer location: This setting places an information bar at the top of your screen telling you the screen coordinates of the last place the screen was touched.
• Show surface updates: Makes the edge of a "window" flash when its contents are updated.
• Show layout bounds: Marks the edges of all the elements in a dialog so you know where any touch will activate them.
• Force RTL layout direction: Forces screen orientation for right to left language support.
• Window animation scale: Sets the speed for window animation playback.
• Transition animation scale: Sets the speed for transition animation playback.
• Simulate secondary displays: This setting allows developers to simulate different screen sizes.
• Force GPU rendering: Forces applications to use hardware 2D rendering.
• Show GPU view updates: With this setting, any view that is drawn with the GPU hardware gets a red overlay.
• Show hardware layer updates: This setting will tell you when layers update.
• Debug GPU overdraw: Overdraw happens every time the application asks the system to draw something on top of something else.
• Force 4x MSAA: This setting forces multi-sample anti-aliasing (MSAA).
• Strict mode enabled: This setting flashes the screen when an application uses the main thread to perform long, intensive operations.
• Show CPU usage: Places a tiny window in the upper right of your screen with information about the CPU and how it is being used. A neat one to play with.
• Profile GPU rendering: This setting can either draw a graph on the screen, or write it to a file. The graph is a visual rendering of how hard the GPU is working. This is another really neat one to try.
• Enable OpenGL traces: This setting watches for OpenGL errors, and places them in the log file.
• Don't keep activities: This setting destroys any and every application as soon as you leave the main view.
• Background process limit: Allows a custom setting of how many process can run in the background at once.
• Show all ANRs: This setting makes every process show an "App Not Responding" dialog if it gets hung.

You can also be "granted" as a developer by clicking on the "build number" label 7 times.

Stock Android: Settings > About phone > Build number
Samsung Galaxy S5: Settings > About device > Build number
LG G3: Settings > About phone > Software information > Build number
HTC One (M8): Settings > About > Software information > More > Build number