What is the difference between a coaxial grounding block, an antenna discharge unit, and lightning arrestor
Antennas can build up a sizeable static charge which needs to be dissipated. Unfortunately the obvious solution of grounding the antenna also removes the signal from the wire. A coaxial grounding block allows static charges to dissipate from the center conductor without interrupting the signal.

More elaborate devices are filled with a gas which is ionized by high voltage spikes to create a very low resistance connection to the ground. This allows lightning traveling through the cable to be arrested. Both grounding blocks and arrestors are discharge units, which dissipate the static charge from the antenna. Only the arrestor provides protection against lightning.

Ideally either would be installed as close to the point of entry as possible. The cable run itself has all the drawbacks of metal suspended in air. It can gather a static charge, and conduct lightning. Also, as the first article points out, you may need a second ground wire if the antenna is atop a metal mast. Though the mast can be connected directly to the ground, since signal loss isn't an issue.