Do I ever REALLY need to shock my pool?

Friends,

So for nearly two decades now I've been running my in-ground plaster pool with good success, but during nearly every season I've struggled with algae and thus had to shock periodically (here in Florida particularly after heavy rains which we have every year, including this one). This year I finally broke down and bought an automated pool cleaner (the Polaris Sigma) and since that time my pool has not only stayed clean, but remarkable stable.

My chlorine levels are always good, my Ph is always balanced and for going on five months now the water seems perfect. But I'm wondering - should I still be shocking the pool? I'm using chlorine tablets that have all the same ingredients as the shock (five different kinds of things including the chlorine) but I was using them last year and still needed to shock. But this year it just doesn't seem like I ever need to.

Am I just lucky or does running my Sigma frequently (which also cleans all the steps and the waterline) keep the algae in check better? If lucky, then should I be shocking once a week like I did last year, or can I go less often (it costs quite a bit for the shock stuff so I was trying to save).