RS vs DEX

So I know me and my players will to often think of using Dex instead of RS. Other than making up you initiative modifier when is s good time to use RS? <div><br /></div><div>I was considering using it as a stat check they roll instead of the -3 initiative mod for having weapons holstered. Like in round one of a fight assume people have shouldered / holstered weapons unless they are clear about it otherwise. And have them roll initative normally but before they get to shoot they have to roll RS. If they make it they can draw and fire quickly. If they fail they don't get to get their shot off and failed any chance for opportunity attacks. Basically reducing their shooting attemp to pull out and ready your weapon action. </div><div><br /></div><div>Bad idea?</div><div><br /></div><div>When do you choose RS instead of Dex?</div>