For example at least in my country, if you want to visit in the parliament as a quest, you have to go through metal detectors. I would assume that this happens also in high security areas in the sixth world. So, we can assume that visible weapons (even hidden weapons) are sometimes a real problem. Pistols offer still options (e.g. shiawaze armament puzzler) even in mad detection environments. But automatics not.
Moreover, if you need to use a guard's weapon (you have not own weapons at all), it is more probably a pistol than an assault rifle. And if I imagine a typical face in his work, pistol skill is more reliable than automatics. But this may depends on your table and campaign => it is not possible to give a general rule which fits in all situations.
