Instead of Shepard dragging Garrus around everywhere in ME1 because she wants to take him under her wing and teach him, I think it'd be a lot funnier if she drags him around everywhere because he comes pre-trained.
I mean, think about it. By the end of the first visit to the Citadel, besides Ashley and Kaidan (who are full members of the Alliance military), she has/is heading to recruit the following:
Wrex, a krogan mercenary who definitely doesn't have a file and who later admits mainly works alone and/or in very small groups, and has definitely not been part of any formal military structure or anything even remotely similar
Tali, who is a very wonderful person and very knowledgeable about the geth, but is only ~22 (her birth year is 2161 apparently), is on her people's rite of passage, and has never been formally attached to any kind of command nor has had any formal training as far as we know
Matriarch Benezia's daughter, Liara, who they know very little about at the moment other than she's an archaeologist who specializes in the Protheans and has never had any commando training, nor do they know if she even knows anything about her mother's actions
I love them, but they're not exactly on the level someone that's been part of a military for years would be.
Garrus, who's not that much younger than Shepard herself, was part of the turian military for a few years (and had at least one ship posting from what we know from 2), and has also been part of C-Sec for awhile given he's a full fledged detective, so he's used to working in teams and being under someone's command
I feel like Shepard would have taken a look at his file and breathed a sigh of relief because there's at least one person that she won't have to worry will accidentally undermine her authority. He even comes with amazing sniping skills and tech expertise! Of course she's going to drag him around everywhere!