teabagyokel really? Scoring three away at Stoke is as valuable as three away at Barca?! Sorry off topic!
OK, Jos.
In the Champions League away goals are counted at the end of normal time at the end of the two fixtures.
In the League Cup (and play-offs etc.) away goals are counted
NOT at the end of normal time but at the end of extra time.
This means that the Champions League does not recognise that goals are equal, causing teams to play defensively at home rather than offensively away, thus not improving the spectacle. No longer is away play the disadvantage it was in 1955 when the rule was codified.
Last year, Arsenal were knocked out of the Champions League by Bayern, having won 2-0 away from home. Can it be honestly said that they had performed poorly away because they had kept a clean sheet against the European Champions? Arsenal had faced equal periods of time (in theory) home and away against Bayern, scored an equal number of goals and been arbitrarily eliminated.
However,
after extra time a team has had
more time away thus has a disadvantage. The introduction of away goals here nullifies that home advantage for the extra half hour. It works - how much better as a spectacle was Manchester United vs Sunderland for the extra period?
The Champions League away goals rule is unfair - it gives two teams with equal opportunities to compete and who finished equal an unequal result. The League Cup one negates extra opportunities with a counter-balanced advantage.
Put it this way, FC Bayern won last year's Last 16 Champions League match, and thus took the opportunity to win the competition as a whole, because they could not attack at home as effectively as Arsenal could, from the other point of view.