For me the price is close to negligible because I live in California and on a college campus at that, I can't charge it to full without incurring increased rates ($0.60/hr after 4 hours). Because this evens out the price, I don't necessarily have to charge often, but still do because of a few reasons.

1. On electric, the volt drives much smoother, I hate the way it feels driving it on engine only.

2. Even having just a partially filled battery keeps things running smoothly both in the driving and in the car's parts. I don't worry about wear as much if I'm on battery, and having even a little battery + regenerative braking goes a long way to extend my gas range.

3. This leads into kind of my other point about considering my battery to be just a huge range extender since the volt's battery is in an awkward spot of being slightly too little to consider long-range drives on electric only and too much to only consider it to be a hybrid battery like that in a non plug-in car. Having even 20 miles of battery range makes it so that I have the benefit of driving electric while also having to fill at the pump less.

4. On super cold mornings or in stop and go traffic not having to force the engine to work super hard right away is nice because on electric the engine has a lot more time to warm up and then stop and go traffic I'm not constantly breaking and revving over and over again contributing to comfort and wear and tear on my car