My sleep schedule isn't good enough for charting, but I did just start using OPKs, for the same reasons that I would chart if I could. It takes the guesswork out. Even with strong ovulation symptoms, it's hard to pinpoint, cycles can vary by a couple days from month to month, you may have more or less CM, and so on. Using a more scientific way of tracking lets you know more precisely when you ovulated, so you can better track DPO, and if you're like me and sometimes have months when you really have to schedule in the BDing, it lets you know when you can safely relax. And I'm sure if I did chart, I'd be watching obsessively for implantation dips and all that. Temping is also one of the most reliable at home indicators that you actually ovulated, instead of just tried to ovulate. It can also be useful information for your doctor if you do have fertility issues down the line.
It really just depends, though. Some couples are going to BD every other day no matter what, and aren't going to test until a missed period, and in that case, maybe it doesn't matter so much exactly when you ovulate.