Are All Windows 7 Updates Important And Do They Slow Down The Computer

I was also thinking if an update is installed for a certain program, and than later there is another update, is still important the previous update? Or it just slows down the computer?

Does uninstalling all the updates, cleaning the registry, temp files and so on, and than installing again all the updates again, speed a little the computer?

P.S. I’m also interested in any kind of suggestion regarding the updates and how they affect the Windows speed & performance!