If it were Ricky Ponting he'd wouldn't enforce the follow on. Most other captains would.
Australia can still come back. Would prefer if they did follow on, build up a lead of 300 and take it home.
2005 England enforced the follow-on and only just chased down the 100+ runs target set, losing key bowler Jones early in the follow-on.
You shouldn't just enforce the follow-on because you can, you have to take into account factors like :-
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Time. Is there enough time to bat again? In this instance we have THREE days left, England should only need to bat 3-4 sessions to add 250-300 and set a massive target. It might depend on the weather forecast and............
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Size of lead. Is it enough to win the match without having to bat again? I doubt the aussies would be bowled out twice for around/under 200 so the chances are England would have to bat again. Time would be an issue whoever batted third, either way you would probably have to fit in two innings although England would know how many runs were needed if batting last
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Fatigue. Having your bowlers in the field in consecutive innings can hold you at a disadvantage. If you bat again then your bowlers are fresh and their side demoralised from fielding. If you enforce the follow-on are you going to get the best out of your bowlers and fielders?
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Batting Last. Generally you want to avoid batting last, part of the sizeable advantage of batting first is you don't and get the best of the pitch for batting.
For me it is better to bat the opposition out of the game, the only times I would enforce the follow-on is a) when it is say 300+ lead or b) when there is not enough time to bat and then bowl. At the moment if the aussies were bowled out fairly quickly for a deficit of say 225 then England would want 4+ sessions to bowl at them last and say 3 to bat them out of the game. That leaves 2 sessions spare to bowl or for possible bad weather, not forgetting they try and squeeze in time made up which in the middle of summer should be ok as long as the weather holds.
I must admit I was gobsmacked at the aussies collapsing, some VERY poor strokes indeed, some poor hooking and very un-aussie like shots. Are you England in disguise? Poncing might have got a dubious decision, bet he's kicking himself for not taking five lower order England wickets in over two sessions and something like 60+ overs. We can't expect the aussies to fall apart like that in a hurry.
There was something in the back of my mind made me think batting might not be that easy though. Despite an opening stand of 196 England did get away with some shots and the aussies did bowl some good balls. Both Cook and Strauss could have been dismissed a fair bit earlier than they were. England should still have made 500+, some of the dismissals in both innings so far have been decidedly poor. I wonder if Broad's two late wickets will be enough to save his place, second innings may be his last chance to do something with the ball.