OPKs only tell you if hormonal changes are taking place consistent with ovulation. They don't tell you whether you actually ovulate. Temping can help confirm whether you are, in fact, ovulating because most women will see a rise in their base temp after ovulation occurs. So, temping can help confirm that you are actually ovulating and can help pinpoint when it happens relative to your positive OPK. Once you see the rise in temp, ovulation has already occurred.

For me, I had a very short window from when my OPKs tested positive to when my temp rose - like 12-24 hours. And I am somewhat irregular and ovulate late in my cycle, so I found temping to be a huge help in addition to the OPKs when we were TTC for #2.

Just to try to get a more precise window to time sex, I think. I hated temping so much. If you're having plenty of sex during the fertile window then you're probably doing enough (use preseed lubricant!)

I've also heard about a new device that is basically a fitbit that measures your body temp while you're sleeping and tells you when you're fertile. It sounds cool.

When the OPK turns positive, it's not a black and white change, but progressive, and around ovulation time, you could even miss the peak if you only test once a day. If you have excellent temperature-taking habits (always at the same time, not getting up, or even stirring much in your bed before taking your temperature), the temp curve can be absolutely beautiful and very obvious.
That's my experience.

If you're already doing OPK's, what's the added benefit of temping as well? Thanks in advance!