One great reason to root your device and add a custom recovery is the ability to continue to update your device long after the device has been end of lifed by its OEM. CyanogenMod has been providing older devices with the latest and greatest versions of Android for years. The latest lineup of legacy devices to receive CM13 include the Motorola Moto MAXX, Galaxy S4, Galaxy S5, and the Galaxy Note 8.0 Tablet.
This will bring all of the devices mentioned above to Android Marshmallow! These are all nightly builds for now which means that they may have some bugs. You may want to avoid using these builds as daily drivers for now as all features may not be functional.