I was watching the 2002 TdF last night and a stage that stood out even more than Rubens Bertogliati's pack surprise on stage 1 was Jaan Kirsipuu's stage 5 win. He was part of a 5 man breakaway, and once it was clear they were going to make it to the end he was the overwhelming favorite for the win. As soon as they passed the red kite no less than 4 attacks went, one immediately after the other. Being the only true sprinter in the group Jaan was going to have zero help, something the other 4 riders were all counting on. What they weren't counting on was him being able to cover each attack and still have something left for the finish. The 5th attack resulted in a two up sprint that Jaan won by about 3", and you could see he was totally blown crossing the line.
I mention this for two reasons: 1) it was an incredibly exciting stage and 2) it shows the importance of being able to repeatedly put in an all out effort in a very short time. Most of us only experience this in crits, but it's still an important thing to have in your repeptoire, that ability to attack, recover, attack, react, etc.
It can mean the difference between making the front group, keeping contact with the main group, or even hanging on to the tail end and finishing with the pack. It's incredibly important and often under utilized in my estimation (especially by me in the past).