To add a directory to a system-protected directory. It's all about protecting the integrity of the installed system. If you don't like/want it, you can reboot into recovery, disable it, and leave it that way.
> It's all about protecting the integrity of the installed system
Why is this important? It's trivial to reformat my drive and have a fresh install. The stuff I have that's actually sensitive is in my home directory and still unprotected =/
Your system is much more secure with SIP in place because it makes big parts of your system immune to trojans and privilege escalation attacks, the two biggest ways malware creeps into your filesystem. It's not very difficult to disable (even permanently if you are inclined), and offers a big security boost.
And yes, it is Apple "Gatekeeping"... the same gatekeeping that's kept OS X almost completely free of major hacks for over a decade. I don't consider that annoying but to each his own.
