In theory:
* they aim better, both in terms of direction and intensity of the pew pew beam
* don't get tired and are relentless, they just react as programmed
* they don't have emotions
* have sensors that can assist directly
* the people otherwise needing to be trained to hunt can be repurposed for other things
In reality:
* one robust EMP would trash 'em with ease (and anything else around them indiscriminately, depending on shield levels any computer might have)
* they can run out of fuel, which is why that's never brought up - apart from the one or two times when they drink an analogue of fuel or have self-regenerating hamsters spinning in their chest cavities
* they can look more formidably as well as more functionally scary
* and yet they sure do look cool, do they not?
* are science fictioney
* prior to the 1980s had stilted staccato robot voices that were sometimes cool
* they sell more collectible toys (as opposed to being thrown away)
* have an aim worse than stormtroopers (never mind the one-off where it's implied the rebels were allowed to escape)
* used for loooooooooooooove in some shows

and lead to jokes in sci-fi comedies like
Red Dwarf how machines are better than people in "other" ways LOL