So are there any benefits from clean install?
Because i dont want to spend 5hour to do that and than nothing is better.
I hope that time machine works on el capitan. Anyone can confirm ? Thanks.
Time Machine works.
There is no tangible benefit to a clean install, it is almost entirely psychological (i.e. the feeling of having a clean slate and no redundant user data on your disk). The installer makes sure that old system components are updated and unnecessary components are removed. El Capitan will actually clean up your /System, /bin, /sbin and /usr folders by moving everything that is not part of the system image out of these locations. Upgrading should thus be a bit of a clean install. Old logs and caches are cleaned up automatically anyway and old preferences and application support files can be easily cleaned up as well (even though the effort is hardly worth it).
The only reason why I would recommend a clean install is if you installed software in one of these locations mentioned above, as El Capitan will break them without a timely update. A clean install could be a way of getting rid of broken applications so that you can start fresh. However, if anything was added to the locations above, El Capitan will get rid of them for you and place them in your home folder.
In sum, unless you have specific issues that a clean install can resolve or don’t like redundant files in your library and user library, a clean install is not worth the effort. You won’t see performance benefits either.
absolutely yes, I don't want my mac to have graphical issues due to some conflicts between old gpu drivers, OpenGL/OpenCL and the new Metal thing
Have you actually any proof that this is the case? Seems to be a widely held belief.