Away goals carry an immense weight in the Champions League.

They delivered Milan to the final in 2005. They saw Liverpool oust Barcelona in 2007, despite the latter winning the leg at Anfield. And they pulled Barca’s fate from the abyss in the 93rd minute in this past Wednesday’s controversial leg at Stamford Bridge.

Added to the competition in the late 60’s, the rule is designed to encourage visiting teams to attack at the other side’s ground. Benfica were the first side to advance on the rule after a 1-1 aggregate score against Glentoran FC in the 1967-68 season when the rule was only applied in the first two rounds. In the 1970-71 season, the rule was finally applied to all rounds. Panathinaikos advanced to the final after a 4-4 semi final scoreline against Crvena Zvezda. Prior to the introduction of the rule (and the introduction of penalty shoot-outs) matches would go to a third leg and then be decided by a coin toss, as when Liverpool advanced after three drawn legs against FC Köln in the 1964-1965 season.

The question seems to arise each season: do we still need this rule?

Arsene Wenger spoke out against the rule at the beginning of this season. ‘I personally feel the weight of the away goal is too heavy now tactically – it was created 42 years ago at a stage when the teams that went abroad just defended,’ Wenger said. ‘But now when you play in your own stadium without conceding you have a good chance to go through. So it has reversed the situation.’

But when Chelsea visited the Nou Camp in the first leg of the semis, they acted as if they were playing before 1970. They went abroad and just defended, with no concern for the great advantage the might have earned by scoring an away goal. While the horrid refereeing in the second leg will continue to dominate the headlines, the Blues’ failure to attack Barcelona in Spain was their true undoing. They showed we clearly still need this rule in the Champions League.

Since the 2003-04 season, 19 of the matches between the end of the group stage and the final have resulted in draws after 90 minutes of play. 11 of those were decided by away goals. Most supporters will agree, penalty shoot-outs are the least satisfying way to decide a match. Does anybody want to return to the coin toss? No? Me neither.

The away goal rule ensures that a match will only go to penalties under the very specific circumstance that both sides are drawn with the same number of away goals. Since it is generally harder to score in the other team’s stadium, this rule remains less arbitrary than deciding a match based on how many times the goalkeeper guesses the right direction in a series of penalty kicks.

To cite the old cliché: it is still a level playing field. Each side has the chance to score these weighty goals. A 2-1 away loss becomes a decent result. A clean sheet at home becomes a serious advantage. And that 93rd minute blast could just be enough to make the walls come a-tumbling down in your own house.

The away goal rule may prove eternally frustrating for those whose European dreams are undone by it, but it remains the best way to break a tie and reduce the number of penalty kick shoot-outs supporters must endure.