I haven't always. I did with my medicated cycles when I never knew if I'd O or not, plus I was learning my body and all about charting.
For the past year I've had natural cycles and really only temp to confirm O. I start temping when I can tell I'm close to O.
I'm not worried about the coverline if I know when I O'd. I can add it. I have enough history to know what is normal for my temps etc. If I'm simply temping to confirm O rather than obsess if it's a pg chart or not

, I really don't need the horizontal line, imo.