I really want to like beams, but... beams are generally bad or underperforming in Starsector because they hit only for low amounts of soft flux, making them useless to attack most targets. Even against targets that are vulnerable to beams, other weapons are often better because they kill faster. With timers that prevent indefinite kiting and stalling, killing speed is important.
Beams are decent against missiles, but with such terrible DPS, Vulcan and Flak beat them by far. Even IR pulse laser with IPDAI and high skills may be better than beams at times.
Beams are good at murdering fighters, Hounds, and Cerberus, but they are generally less threatening than most. Few ships can stack enough beams to murder more.
Beams are okay for ships that do not have any better options for energy mounts. For example, Eagle's turrets are set so far back that some attack that can match the range of your ballistic points and hit for weak damage is better than no damage at all. (If you use pulse lasers on Eagle, your range is so bad you might as well go all the way for melee with HMGs and Safety Override.)
Weak, long-ranged beams (i.e., tactical laser) are a cheap way to poke the AI and fool it into keeping shields up (and prevent their hard flux from dissipating). Alex is aware of this exploit and has hinted that may get patched next release.
Ion Beam is very good, because it can pierce shields and knockout stuff. However, it is such a flux hog that your ship cannot support more than one or two.
HIL is nasty if it is not blocked by shields, but few ships can combine the HIL with another long-range attack that hits for hard flux.
As for the OP, Graviton Laser is like a heavy tactical laser, though not terribly good at it, but it is a bit better if you have the OP to burn.