ALso how does checking cervical positioning help??
Well, this is a personal question. I like to know what is going on. I like to pinpoint the day I ovulate and be able to accurately count my luteal phase so that I know when would make sense to test, when to expect AF, and then beyond that, know if I'm pregnant and have an accurate conception day for dating the pregnancy. I don't like being in the dark when AF is "late" which can happen if you don't accurately pinpoint your O day. I also enjoy charting- I think it's fun. But all this is just me. Other women find it stressful and prefer to go with the flow more. If you're DTD every other day throughout your fertile period and a bit beyond then sperm will be present when the egg is released, which is of course the goal, but your counting of days past ovulation may be off so you may have some question about when to test and when it should be accurate. Also, if there is anything of concern happening with your cycle like a short LP or pre-AF spotting it can be helpful to know exactly how many days are in your LP.
OPK's are often unreliable for a lot of women, so they can be frustrating and end up being expensive. Plus they cannot confirm O, just that your body was gearing up to O. So you can end up missing your peak fertile days. But since you are tracking your CF then you would know to keep DTD if you see a second patch of fertile CF even after your last OPK+. It's just with temping, you would already know if your body O'd or not.
As for CP, that is a helpful addition to a chart that is not completely clear. If you get fertile CF, but have unclear temps, your CP can help pinpoint O better. But if you have a clear temp spike, CP is not necessary. CP could be helpful, too, if you're NOT tracking temps. For example, if you get a second patch of CF after your last OPK+, you could check your CP as well and see if it's high and open. If it is, you might assume that you are now gearing up to O. If it's low and firm, you might assume that this is just some random CF and you did in fact O earlier.