Combat option?
 

What does this mean: If checked. A special effect will be played whenever a responsive skill is available for use?'

I turned it on in hope that it would flash something mid screen or play a sound when one of my skills was ready, but noting happened. :(

From what I've noticed, its a very unannounced effect while in combat - not nearly enough to tell when one of your reactive skills become available.

It's supposed to alert you to when you have a skill ready that is based off of a parry or dodge in combat.

Its a colored cirlce that flashes above your minabar and plays a a sound