How does having a teammate in a breakaway benefit a cycling teams leader?

Answer 1

There are at least two takes on this question:

Riding at speed, air drag AKA wind resistance is quite high. If you're a solo rider, you have to battle all that wind, all the time, by yourself.

If you have a team mate along you can take turns riding point and resting in the pocket of still air just behind the other rider. Means that two riders can either go faster for the same amount of effort, or equally fast at less effort when compared to a solo rider.

The other take is mainly applicable to multi-stage, team racing events. In a multi stage event, overall win is calculated on points, with most points going to the stage winner and then a diminishing scale. This means that if you're consistently placing high, it's possible to win the race w/o actually winning a stage - assuming that there are always different guys getting the top spots.

So let's say you're in a team with a guy in a good position for the overall win, and a strong contender takes off in a breakaway.

If you manage to get a good, but basically disposable rider into that breakaway, you can instruct him to try to steal the win from the contender at any cost. Preventing the contender from getting the highest score will help keep your team's strong rider in a good position for the overall win. The "disposable" rider can put in a greater effort, as he knows there's no pressure on him placing good on the next stage. The contender can't really race as hard, as he has to be in shape to compete during the next stage too.