The training montage is one of the greatest film cliches of all time. This is the point, somewhere in act 2, in which the hero/heroes have to get better at whatever it is they suck at. Say a group of teens need to breakdance fight some anonymous corporate goons to save an inner city rec center or whatever, well you're gonna need a montage. It's the only way to condense months of intense training into a 90 minute movie. Both great films like Rocky and Chariots of Fire and crap movies like Step Up and Bring It On Again have a training montage. At the beginning, we see a hopeless yutz getting incrementally better until they are the greatest athlete/dancer/warrior ever in just 7 minutes. You know, like in reality.
The guys at Slackstory put together a montage of movie montages and set it to the perfect tune: You're The Best Around from The Karate Kid. Sweep the leg!