Punter57,

I can only try to explain one way I use POT by using an example.
I use a computer based system on West Aussie races which I've bored people with on this forum before but it gives me, year by year, for the years 1999 to 2004 the following POT:
6.98%, 0.55%, 9.7%, 12.81%, 6.08%, 7.17%.
This is over a couple of thousand races a year so the figures shouldn't be too wobbly and I should feel pretty safe that I won't loose a lot of money, in fact probably gain some. Based on this and a few other figures, like longest loosing streak, how much money the missus will allow me to divert to a bank, etc I can work out how much I feel like investing and estimating a POT of four or five percent how much I might finish up with in a few year's time.

I take POT a lot further than this though breaking it down by track. At Ascot races the corresponding POTs are:
-3.81% -8.53% +11.1% -25.45% -18.2% +2.86%.
and at Belmont:
+22.82% 9.54% 1.28% 29.92% 19.49% 15.73%.

This is certainly helpful in deciding the size of my bets. They are 0 at Ascot where I've come out behind year after year and as much as my weak heart will take at Belmont where I win year after year.

Up until about April this year my POT overall for all tracks was down as far as -12% but I didn't freak out and stop betting because I was confident it would come back based on many previous years positive figures. Sure enough a bunch of better bets has now boosted it up to +5.04%.

This is only a very coarse outline of how I use POT but I'm sure you must gain some insight into its usefulness and how you might use it to decide at least whether some bets are worth making at all and maybe eve how much you might be willing to stake.
If not IMHO (In My Humble Opinion) either I don't understand what you are trying to understand or you're just being perverse.
Either way, may your POT always remain positive.

Kenny