This technology got its start in docking bays before it became militarized. Since then, magnetism has gained favor amongst Sages as a means of manipulating the velocity of ships. By rescripting the "newtonic tetherae" (yes, this is a legitimate preterscientific term) that impose the law of equal and opposite reactions, Sages are able to pull ships great distances and at great speeds consuming very little energy. This use of focused magnetic power is commonly referred to as "carrot-on-a-stick magnetism." There are even stories of Sages using it to tow planets.
It's much easier to see this ability in-game than in a still picture. Look for pulses of what looks like space dust being drawn towards the ship using this ability.
A ship actively turning and thrusting away from you can easily break out of the field, but it can be quite an inconvenience for ships that are dependent on precise maneuvering or which already have mobility problems.