"Battery Saving" Apps are used to reduce battery usage on your Smartphones. The basic idea of this apps is to kill or "Force stop" the apps which are running at the background which consumes a lot of memory. The more the memory usage the more battery will be consumed.
First thing I wanna clear is All Depends On Your Usability.
l.e. if you only use WhatsApp, Facebook, or any other lite apps then it doesn't matter its quad core or octa core you can't even able to use at least 2 CPUs of quad core.