I just don't think that's a very good answer. Mass Effect is basically a "ticking time bomb" story: there is a hidden threat to the galaxy, only the hero can stop it, and the time to stop it is rapidly running out. Sheppard doing loyalty missions while the galaxy inches closer to catastrophe would be like Jack Bauer taking a break half-way through a season to help a buddy connect with his kids. It's both a question of plot and of pacing. I also don't think "the Illusive Man hasn't told me what to do yet" is a very good reason for Sheppard to sit around doing nothing. Sheppard has the fastest ship in the galaxy, is armed to the teeth, known and respected everywhere, is best friends with the shadow broker, and the reaper threat draws ever nearer. Surely there is something productive Sheppard can do beyond helping crewmates with their emotional issues.