That method works great! And no you will not lose anything. But like the person above me said, do your homework and make sure you know what you're doing.
Good luck, and enjoy your root access
Oh, and while using the casual root method, go ahead and unlock the boot loader and flash CWM recovery right away. Casual will do this all for you. Just choose the options from the drop down menu.
It'll save your a few extra steps in the future if you ever do decide to try out a custom Rom someday.
Sent from my 16GB Blue Verizon Galaxy S3 running MIUI v5 with KT kernel
16GB Blue Samsung Galaxy S III (Verizon)... With a different ROM every couple days....
Custom Built PC- Running a tweaked, de-bloated Windows 8
Dell Studio Laptop- Running Ubuntu 13.04 (sold)