system
Given the following post, respond as if you're commenting on Reddit:
human
[Mass Effect] Why does Shepard only ever take 2 people with her on missions?

At least in 1, it's not a limitation of the Mako, since on Feros we have an extra person along for the ride. Some missions of course require some more subtlety, but some really would benefit from more firepower. Hell, in 2 they have to get all your companions off the ship on a mission so the collectors can attack.
gpt
Mission parameters dictate a small strike team would be most effective give the proximity to superior hostile forces. 3 soldiers draws less attention than a full squad would. And bringing 3 capable fighters can handle most threats long enough for reinforcements to arrive from the Normandy. Stealth and precision is the goal of Spectres not overwhelming force.