An afterburner, when ignited, accelerates the spcecraft, thereby allowing it to reach a higher velocity, escape from capital ship turrets, and run away from hostile sentry defenses.
The rate of acceleration is dependent on the type of fighter or bomber. Each craft has a maximum speed, both with and without afterburners. While interceptors are generally faster while on afterburners, bomber engines tend to be slower, instead focusing more on shields and weapons.
Any ship using afterburners can be recognized visually without reading the target's speed on your HUD. When the afterburner is used, the engine glow changes color, often to a lighter saturation.
Increasing the energy diverted to engines also allows afterburners to recharge more quickly. However, having no power on engines causes the afterburner to not recharge.
The PVF Anubis is the only canon fighter without afterburner capabilities. However, a number of Shivan bombers, notably the SB Shaitan, the SB Seraphim, the SB Nephilim and the SB Taurvi, also lack afterburners.