The major advantage of this technique compared to other space propulsion systems is that it doesn't require any chemicals. The energy gained by these tether systems is stolen from the planet's spin. You're spinning down the Earth. As well as generating power from nowhere, electrodynamic tethers can be used as a brake. If the Lorenz Force current is not forced back down the tether, the upwards-travelling flow comes at the expense of the orbiting platform's momentum.
Kinetic energy is converted into radiating out into space along the length of the tether.
This energy theft will eventually slow a satellite down until it is unable to circle fast enough to sustain orbit. It will drop and burn up. Left alone, a dead satellite can take months or years to fall out of orbit. The idea is that all satellites will eventually contain a system for periodically checking whether the vehicle is still fully operational. If not, the terminator program will ask its ground control for permission to initiate termination.