"A multi-barrel machine gun with an extremely high rate of fire. Mechanoid-built."
Miniguns are excellent crowd control weapons. Their miss radius and extremely high DPS are valuable assets when it comes to crowd control, especially in later game when there are many more enemies in raids. If you manage to get multiple miniguns to your name, you could possibly have a great deal of firepower on your side, but also a high risk of collateral damage if within your base, dependent on setup.
The minigun is even more powerful if equipped on trigger-happy colonists, as they have a 50% reduced warm-up time, allowing them to fire much faster; the accuracy penalty is completely irrelevant for this weapon as it has a forced miss radius. This forced miss radius won't change whether the minigun is worn-out and of awful quality, or pristine and legendary; quality also bears absolutely no relevance to miniguns, and lower quality will actually be better because they won't affect colony wealth as much.
It also functions as an excellent quasi-melee weapon, rapidly ripping the enemy to shreds at point-blank range. This works well especially when you are facing a manhunter pack with large animals such as elephants or rhinoceros, often killing or downing the poor animal with 1 or 2 bursts, while melee weapons are much slower.
Despite all this, it may be impractical to use outside of point-blank to very close range combat (even with higher qualities) against single or highly spread out targets due to the insanely quick accuracy dropoff and forced miss radius. Sometimes it may be a better idea to sell it to suppliers who will pay quite some money for one, or smelt it for a little steel.
A single centipede armed with a minigun is almost trivial to deal with if engaged at even medium range and behind a wall or sandbags, simply spreading out sufficiently, or distracted with lone colonists; stack up multiple miniguns with Inferno Cannons and Heavy Charge Blasters and things can quickly get out of hand without killzoning, (ideally at least 6) mortars or just outright raw firepower.
Besides mechanoids, heavy mercenary raiders may also be equipped with a minigun.