To me it's like tires, why wait to replace them when you are bare and hydroplaning all the time when we all know you can drive them till they actually blow out. There's probably a few thousand miles of extra use in there. I don't consider it wasteful to replace them prior to blow out, I hate changing flats on the side of the road more than I hate wasting that last thousand miles. Most of us replace tires when the risk of continued use rises beyond a threshold, even when there are clearly a few miles left on them.
I find this decision is similar to when to buy gas, do you drive until it stops running, or get fuel prior to running out? Some get fuel prior to the low fuel light/warning, some right after, and some push it. I tend to push it a ways, but I track miles very carefully once the light comes on. I reset my trip counter at every fill up. I've only run out of gas once in the last 500,000 miles, and that was 1 mile from the gas station I had planned to stop at. We don't have the luxury of a battery capacity gauge, but we do know they have a time/use factor. To me, the low fuel (battery) light comes on after 5-6 years, depending on use and battery size. Then I track it's behavior carefully. I'm currently at 5-1/2 years on mine, I'll probably replace it in the fall when it starts to get cold again.
As to it being wasteful, last time I had a car not start (Altima, it ended up being an electrical component failure that I could bypass), it made me 3 hours late for work. At that cost me about $170 in lost wages. The replacement was $65. I'd gladly replace that component in advance had I known it had an approximate expiration date, and I'd be money ahead. I'd also have had to replaced that component anyway, so it's not creating waste.