What are the useful nvram settings in macOS ?

The OS X boot arguments are useful for troubleshooting problems with system startup and how the system behaves when running.

• sudo nvram boot-args="-v" : This command will set the system to always boot to verbose mode, so we do not need to hold Command + V at system startup.
• 
  
• sudo nvram boot-args="-x" : This will set the system to always boot into Safe Mode.
• 
  
• sudo nvram boot-args="-s" : This command will boot the system into single user mode without needing to hold Command-S at system startup.

• sudo nvram boot-args="iog=0x0"  :  when you close the display but connect the system to an external monitor and keyboard the system will stay awake. After running this command, when connecting an external monitor, the internal display will be disabled, which can be beneficial in some situations such as those where you are mirroring your desktop but wish to run the external display at a higher resolution than your laptop can run.
• sudo nvram boot-args="debug=0x144" : a combination of kernel debugging features that will show you extra information about the kernel's processes, which can be exceptionally useful if a system is experiencing kernel panics. 
• sudo nvram boot-args="debug=0x14e" , this will display even more logging options. The primary use for this is that it enables old-style kernel panics that show scrolled text on the screen about why the system panicked, instead of displaying the gray backdrop and the message to merely restart your system. 
• 
  
• Additional debug options are as follows, though these will likely only be useful to kernel programmers:

* The option DB_KDP_BP_DIS is not available on all systems, and should not be important if your target and host systems are running the same or similar versions of OS X with matching developer tools. 

**The last option DB_LOG_PI_SCRN is only available in Mac OS 10.2 and later.