I wouldn't be telling you if I wasn't serious . VS needs all original components to be installed at the time of the initial installation. It's the same with upgrading it. The upgrade really isn't an upgrade at all, it simply an uninstall and reinstall of the entire program.
There's not much of a reason to other than maybe saving a few minutes and decreasing resource consumption during installation. You can save all your settings for VS and load them later and project folders are easily integrated on the fly.