Yes, I’ve read similar descriptions about ‘station keeping’. Something about this gravitational well or neutral point is significant in making orbital characteristics favorable but I don’t get the intuitive mechanics.
They are obviously not going to have a continuous fuel vector. Or maybe they will.. and only need a very tiny bit. But 10 years of doing that?
Basically, it’s a “saddle-point” (flat spot) in the gravitational potential field for orbiting objects. At the L2 distance, the spacecraft “sees” the gravity of earth and sun added together, so it can orbit a million miles further from the sun than earth, but still take the same 365+ days to orbit the sun that the earth does. It’s a “cheap” (in terms of fuel) spot to hang out and still maintain (about) the same distance from earth at all times.
I am not an engineer, but my take is that orbiting something that is in constant and slightly unpredictable motion requires less energy than trying to maintain an exact fixed distance from that same object.
There are also practical advantages for a telescope.
Relative to Earth, Webb is in a polar orbit around L2. The length of its orbit - north and south - is slightly larger than the orbit of the Moon - east and west - around Earth.
This solves two problems. First, Webb will never pass within the shadow of the Earth or Moon. A shadow would mean fluctuating electrical power, plus, temperature sensitive equipment would be constantly heating and cooling.
Second, Webb will have its insulated back side permanently facing the sun as it orbits, which means it can work 24-7 with an unobstructed view of the universe (every 12 months) except for the tiny piece of real estate between Earth and the Sun.
The executive summary is something like: there are various reasons why it's better to be close to L2 rather than to sit still at L2 all of the time. More sunlight (not in earth's shadow), better communications coverage, easier station-keeping, etc.
Once you offset from L2, earth's gravity "pulls" at an angle. That pull can be viewed as the vector sum of a component toward the sun and a component perpendicular to it.
The perpendicular component is the "pull" that keeps Webb in an orbit, just as though there were a real object at L2 to orbit around. (The toward-the-Sun component, of course, keeps Webb in an orbit around the Sun.)
Webb's orbit around L2 is very large; bigger than the moon's orbit around earth. It takes about 6 months to make the full trip around.