Water cooling allows your rig to run more quietly in addition to clocking higher. Plus, I find water cooled rigs to be more aesthetically pleasing (if done properly). It's a hassle if you don't like to tinker with things, but it's fun for an enthusiast.
'Watercooling' is not a pseudonym for 'overclocking', so let's make sure we're not making this assumption. You can certainly do one without the other.
Also, with a full cover watercooling block, you might see 30-50% reduction in core load temperatures on your GPU. It's rather substantial to go from seeing 85C temps down to seeing 45C temps at load with a proper loop setup.