You can read the brief description here - http://www.oreillynet.com/onlamp/blog/2007/11/policykit_looser_limitations_t.html
And, you can scroll down to Permissions and Encryption here for the alternative - http://ubuntuforums.org/showthread.php?t=510812
Since the development is from RedHat, one supposes that the need was for the commercial side. It is intended as an Administrator's tool for an actual IT system.
So, everything on the desktop is compromise. If you are going to assume that Windows "transfers" are stupid, then the devs offer up something along that line. And, put PolicyKit on the desktop. And, they talk about "next year, the Desktop, then - the world." A system designed as desktop that hardly anyone uses - except as server.
The other side is that many "transferees" seem more interesting in colors and shaky windows than intestines.
So, you are offered a non-intuitive graphical mess without much instruction. And, if you try to "neutralize" it, it will screw up the entire install. The same "stuff" is offered in Windows in the Professional and above systems. Administrator sets up passwords and account and account parameters. But, in XP (and I suppose the latter versions, you don't have to actually do it. And, it isn't that big a deal as the setup is neat and simple.
So, if you want to learn how to set permissions, etc., do what I suggested above in the first, somewhat strident post. Without going too rad, you could practice on Debian.
If you make much fuss about it, you will be assaulted and further insulted. And, you'll get a harangue such as the one here - http://ubuntuforums.org/showthread.php?t=716201
If you should ever feel the "heat" of such a scolding, just repeat the mantra "MS is evil; Windoze sux" and you recover eventually. You see, the irony is that Ubuntu's first few releases had a routine root setup at install, allowing a root login. They are now like reformed drunks running around screaming - "if you drink too much, you'll get drunk". I use that example since they are rapidly making Linux "free" only as in beer.
There is currently a great rush to "security" within Linux. That can be seen by the recent fix to the kernel wherein a kernel bug of more than 10 years duration was patched. Whoopee! Course, the bug "discoverer" had to be insulted and mocked before a fix was done.
"And then, after installing the kernel patch, Mr. Gnomehead downloaded a delightfully curious and fascinating screensaver which dropped a rather sophisticated bot into his oh_so_secure_Linux box."