ESX Commands – esxcfg-advcfg

Everything I find out in the VM Blogosphere about studying for the VCDX says to know your esxcfg- commands. Ok. So here I go.
The first command as I start out was the one on the top: esxcfg-advcfg.

[root@esxlab1 root]# esxcfg-advcfg
Usage: esxcfg-advcfg []
-g|–get Get the value of the config option
-s|–set Set the value of the config option
-d|–default Reset Config option to default
-q|–quiet Suppress output
-k|–set-kernel Set a VMkernel load time option value.
-j|–get-kernel Get a VMkernel load time option value.
-m|–set-message Set DCUI welcome message.
-u|–uuid Ensure the Vmkernel system UUID is set and print it.
-h|–help Show this message.
-r|–restore Restore all advanced options from the configuration
file. (FOR INTERNAL USE ONLY).

A great wealth of info about this command (and all esxcfg- commands) from b2vGuide2vmware3. So not wanting to repeat anything written on the site. I would ask what is the common usage situation for this command?
We can see how to use the command but exactly why would I do those changes?
I guess from the looks of things this command might be the hardest one to explain.
Anyone out there able to fully explain this?

Maybe alphabetical was the wrong way to start.