Currently I'm using ubuntu 12.04. Previously I've used dual boot (Ubuntu 13.04 / Windows 7), both OS configured with ATI Catalyst Center. But few days back both OS started to crash. Ubuntu 13.04 freezes to death, I can't even switch to CLI. Other OS error log indicated that it was due to Graphics driver. Now I can't re-install Ubuntu 13.04-amd64. Till now 12.04 working fine without additional graphics driver. Is it necessary to install ATI CC, If I continue without ATI Driver does it harm my system. I've 1GB ATI Radeon HD 5470, Please ask if you need any additional info.
The OSS driver (radeon) is coming on in leaps and bounds though. 3D performance in Mesa 10.2 and post-3.12 kernels is pretty good. Not quite as good as the closed driver, admittedly, but if you're stuck with a card that's only supported by the legacy catalyst driver then the OSS driver is a bad consolation prize.
No, it is not necessary to run the proprietary drivers. They are not installed by default. Also, once you do install them, it is not straightforward to remove them.
However, if both windows and ubuntu are crashing, perhaps it is not your drivers at fault but some hardware issue with your graphics card i.e. it is worn out.
I have the same type of graphics card, but I don't have a driver. use s3tc. its a compression tool. start by adding ppa:xorg-edgers/ppa to your ppa list, sudo apt-get update, then go to the software center and look up s3tc and there are 2 packages. install them both, and make sure you run the update manager. I did this, and my computer runs faster and better than ever when playing steam games.