Why disable it? I personally prefer to simply not use it, at least not for every day browsing, I sometimes do use it for testing purposes. In Win 8 they give an option to disable it, so I assume it's safe to do.
If you disable it, some components of IE are still used by third-party programs. For example, a dictionary app you installed may still use IE as its rendering engine since that is pre-installed on every Windows computer.
