I think some are missing an important point here. The decision whether or not to sit deep to try to defend a lead surely depends on how the pattern of the match has progressed to the 80th minute. If we have had much the less of the play,created very little,been penned back for much of the game,and found ourselves 1-0 up against the run of play with 10 minutes to go,then it would make sense to bring a couple of extra defenders on to try to see the game out.
If,however,we have been the better side for much of the match,allowed the opposition to create very little,but our play in the final third has not matched our superiority and we've been wasteful with our chances, and,as a consequence, find ourselves only one goal ahead instead of the three it should have been,there is no logical reason to change our tactics with 10 minutes + 5 minutes added time still to go. On the balance of play,we are much more likely to score than the opposition,so why concede ground to them and invite them to try? The tiring players argument doesn't hold water either....they can be replaced with like for like subs.when you have a squad like ours.