[Q] cm 11 vs cm 12 what's the difference? topic

Hi , I'm entirely new to this rooting & custom rom thing I have the sony xperia m c1904 model. Since sony stopped updating it any further from Android 4.3 I've been researching a little & found a little about cyanogenmod developers so what exactly cyanogenmod 12 differs from cyanogenmod 11 . I've heard it's still in beta or nightly stage so what's more I'll get apart from android 5.0 why cyanogenmod 12 matters? Please explain.....