Ok think you said you had an OAFC win at 3/1 - so say £10 on, returns £40 (£30 winnings plus £10 stake) - £30 profit. Let's make numbers up and say the cash out was £30, giving you £20 profit.
At the same point you could probably have backed the 'double chance' Solihull/Draw for, let's say, 8/1. So you could have stuck a fiver on that instead. If OAFC hold on for the win, you're £25 up (the £30 profit from above, minus your £5 hedge). If they don't win you've lost your original £10, but gained £40 profit from the hedge, so £30 up.
So either £30 or £25 profit, rather than £20 through the cash out.
Obviously made up numbers, but the theory is real