The Multicache Config allows you to configure important parameters to multicache. It works on a last saved state. You will find certain Global Configuration parameters repeated, this is done to bring about uniformity and conformance to the product as a whole. Lets take for example the parameter 'Cache Handler', you can choose to set it either from Joomla's Global Configuration or multicache config. If you do set different states, then only the last saved state will take preference.
You will therefore find it convenient, without having to cross check whether settings have taken shape.