In what cases are optical amplifiers used, and in which optical repeaters?

Question

Computer networks

Theoretically, the differences are clear: the repeater regenerates the signal and high signal-to-noise ratio, the amplifiers are simpler in design, multiplexing of different signals is allowed.
Practice is of interest in which case preference is given in various configurations: as I understand it, at a distance of 400 km, you can apply a circuit on optical amplifiers, repeaters, or even use optics that can such a distance ..