system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] What's the purpose of R2 Units in starfighters, and why do some starfighters, such as TIE fighters, not use them?
gpt
R2 units are called "astromech" droids because they can function as a navicomputer for a hyperdrive in ships that aren't equipped with a full navicomputer. They also assist with repairs, power rerouting, and other computing work. They're basically a copilot, navigator, and pit crew all in one. However, they weigh quite a bit and have been known to develop odd quirks and combative personalities, which requires lots and lots of maintenance to keep in check.

TIE fighters are not equipped with a hyperdrive, as they're meant to be short-range fighter support craft for carriers (such as the Star Destroyer) rather than independent, long-range craft.

Also, there's a pretty heavy prejudice against droids in combat, following the Clone Wars. That the terrorists use them so universally is just a sign of how deplorable they really are.