option clash, because a package can be loaded only one time! And that is done for
beamer itself internally, but without an optional argument. LaTeX marks
hyperref as loaded after the first
RequirePackage and then throughs an error if a package should be laoded a second time with different optional arguments. In such a case a
\PassOptionsToPackage helps, or only for beamer one can use
A user often didn't know what packages are already loaded by the documentclass or other packages or by LyX in its defined preamble. Then he/she realizes only by the option-clash error that a package should be loaded more than once.