Leveraging a Price
If you enjoy trading a market, you will often find yourself left with a bet at a much better price than was available anywhere else, even on Betfair.
In this case if you had backed Australia before the tournament to win the World Cup at 3.5, then as the tournament went on, decided their price was too short and wanted to lay them for much more at 2.3. Compare your profit and loss now... the effective bet is now laying Australia at 2 for £80, a price lower than available at any time so far.
It all comes down to timing. This type of trade isn't going to happen in 30 seconds. Work out a strategy and stick to it. If you are backing something to win, then don't trade out and get angry when they continue on and win. If you are only looking to lock in a profit irrespective of the result, then do it and ignore what happens later. You'll only remember the two winners you closed out early and not the ten losers you still made a profit on - that's the way the human mind works.
Trading isn't just about locking in a profit - it's about putting yourself in a better position than you had before you started (or sometimes even bailing out for a small loss instead of risking a big hit).