The Director, a Quantum AI, has calculated a series of actions both large and small that will mitigate the destruction of the earth and the near extinction of humankind. This is known as the Grand Plan, also referred to as the Master Plan or The Director's Plan.
Some of these actions are quite large, such as in the season 1 episode titled “Helios-685” where the core traveler team deflects an asteroid that would have hit the earth and caused a chain reaction leading to an ice age. Some are not as large, such as protecting a person who will play a pivotal role in the future.
Some missions require an entire team, and some only one or two people, and there is the rare mission that requires teams to work together. On some combo missions, each team's ultimate mission goal is not the same, but they have to work in concert for the overall success.
No mission is unimportant, as each is a key element in the Grand Plan that affects the ultimate outcome.