Personally, I prefer to keep heavy duty augmentation out of my Traveller, but it's certainly present in the Mongoose rules.
We have machine prosthetics in real life, of course, but my preferred science fiction future says that lost limbs and other replacement body parts are grown from cell cultures that are biologically compatible with the patient, and transplanted. At very high technology levels, they may instead be grown in place through stimulated regeneration, but I haven't had occasion to make a ruling on that in my games.
The grown replacements offer some game flavor opportunities too. Suppose someone loses an arm in combat (including a mishap during character generation). Medical technicians take a genetic sample from the patient and either use it to change the immunological profile of a standard lab-grown arm or grow an arm directly from the patient's genetic code. When it is either immunologically adjusted or grown from sample cells, it's attached through ordinary surgery.
Unless the patient pays extra for a cosmetic match, the skin color, amount of hair, etc. may not be a close match to the original. And because muscle condition is strongly influenced by exercise history, it may not match the other arm in muscle tone. For a price, a patient can get a close match, or even a pre-exercised bodybuilder arm, though the latter may require extra effort to get used to and to maintain condition.
So, if a character gets a budget limb replacement, they might end up with a new limb that's pale and nearly hairless because they got the procedure done on a thick atmosphere, orange star world where most people are very pale, even though the rest of their body has very dark skin because they're from a thin atmosphere, high ultraviolet homeworld. Or maybe they have to take dietary supplements to keep their new arm healthy, because it was grown from a standard Vilani genetic template, tuned to their immune system, but not to their metabolism, which lacks some peculiar Vilani metabolic variation.
That makes for characters with more character.
By contrast, augmentations can grant powers beyond natural human range, but they're dependent on high technology repair if they're damaged. That might be acceptable for someone who never leaves a high technology homeworld, but it could be trouble for someone who hops worlds -- particularly if they visit a world where the augmentation is both detectable and illegal.
