The NASA.gov feature Q&A: NASA’s New Spaceship says

Q: NASA’s really building a spaceship?!

A: That’s right! NASA is working with its partners to design and develop a small spaceship that will orbit the Moon called the Gateway. This spaceship will be a temporary home and office for astronauts, just about a five-day, 250,000 mile commute from Earth.

The Gateway will have living quarters, laboratories for science and research, docking ports (like doors) for visiting spacecraft, and more. It will provide NASA and its partners access to more of the lunar surface than ever before, supporting both human and robotic missions.

The Gateway will be our home base for astronaut expeditions on the Moon, and future human missions to Mars. Even before our first trip to Mars, astronauts will use the Gateway to train for life far away from Earth, and we will use it to practice moving a spaceship in different orbits in deep space.

NASA seems to have a substantial degree of competency moving spacecraft in different orbits in deep space already. In what ways will moving spaceships (read space stations) to different deep space orbits require practice?

Possibly related (and currently unanswered): How will the Lunar Gateway go to L2 and L1?