Why ubuntu uses compiz ?

You don't have to use Compiz. You can use any windows manager you like. Unity needs Compiz though so you will not be able to run that shell.

Yes i know that !
But why ubuntu with unity uses compiz ?
I have so much awfull performance with compiz specially on flash videos and 3d games !!
When on other window managers like cinammon, xfce, kde, lxde i have full fps and best performance !

Because it needs it for the effects.

XFCE, KDE, Cinammon and LXDE are desktop environments, not window managers.

If you get a better experience using something other than Gnome+Unity+Compiz then don't use it. I have a media PC that tears when I play videos under Compiz+Unity etc but when I switched to Lubuntu it is smooth, the same system can play 3D games well and uses an Nvidia GPU so should be fine.

I hate Firefox browser too, it chews RAM and crashes a lot, it is the default browser in Ubuntu but like Unity + Compiz, it can be changed. Same mentality.

I know that xfce , kde , cinammon are desktop environments but they have different window managers and compositors (mutter etc) thats why i mentioned them.

I like ubuntu style but video playback sucks i dont know maybe its because is still on beta .
I've tested it with a nvidia geforce gts 250 .....
(very good graphics card , absolutely perfect doing 3d gaming in full res and detail and high fps)
...and i had tearing !! (plus some other problmes bad support!)

I've tested with an ati radeon hd with 2gb of ram and when i turned on the antitearing i had no tearing but frames where decreased very badly !! No way I couldn't watch an hd video normally !!

I think ubuntu got too heavy, and what it sucks more is that uses compiz which makes 3d gaming and full hd video playback... -(flash video playback out of question) - ....a distant dream.

If someone that comes for first time on linux installs ubuntu he will forget completely anything about linux

.....i didn't had these problems before the 12.04 version !

12.04 is stable, only 12.10 is beta at the moment.

Did you grab the 304.51 from xorg updates (less fresh, more stable) PPA. If you think Ubuntu is heavy, my Quantal install is 3.0Gb installed and uses 500Mb with Chrome, Compiz, Gnome, Unity, FeedReader, Mounty and Dropbox client running. I'd love to see what Windows uses to achieve the same thing. Windows7 easy tips 10Gb after updates and installing office productivity, media plugins, CD burning, DVD playback etc. Not light at all.

If you want, you can install Lubuntu or Xubntu and it will run super light

From 12.04 version i have problems with low fps on 3d gaming .
Now on this beta i have problems on video playback too.

Ubuntu with compiz and unity is a disaster everything is slower , applications are launching slower, opengl problems extremely low fps etc etc.
Even if i like it i dont want to use it.
I dont know why it still uses compiz it sucks now !

I'm considering testing some other completely different distros.
Right know i'm using linux mint 13 xfce.

Linux Mint is based on Ubuntu, so not a completely different distro at all.....

Did you try the later video driver?