The various weapons in the game have a variety of stats, but I know that some of them (at least) are only useful to Shepard. For instance, weight. Squadmates are not at all effected by how much their weapons weigh.
What other statistics matter for squadmates though? For instance, adding a scope to a SMG or AR improves its accuracy bar in the weapon stats, but does that change how accurate your squadmates are with them? As they're computer controlled (or in one case, a computer), I doubt that they're really shooting wide or missing distant targets due to a lack of scope.
Squadmates have infinite ammo, so does it matter if their clip sizes or reserve ammo is larger? Do they depend on the "real" reload delay for a weapon, or do they spend a fixed amount of time in their reload animation regardless? Has anyone tested to confirm that damage upgrades actually mean something for them?
Best Answer
Weight: Is irrelevant and can be ignored.
Capacity: While companions have unlimited ammo, they are restricted by the clip size of a given weapon - it affects how often they reload, and, by extension, their overall rate of fire as well as time spent in cover.
Fire Rate: Obviously companions are affected by this. Rate of fire is just as important to their damage output as it is to Shepards.
Damage: Again, this is just as important to companions as it is to Shepard.
Accuracy: Accuracy does matter for companions. Even though it can be assumed that the AI isn't going to fire wide on purpose, accuracy has a noticeable impact on, for instance, the spread of pellets from a shotgun blast, or the level of 'drift' during a sustained burst with an SMG or Assault Rifle.