Single shot has to do with the autofocus settings, not the ISO. Auto ISO will use your metering mode to determine exposure with the mode you have dialed in to expose what the camera thinks is correct.
Adjusting the ISO manually vs auto has its benefits and its downsides. Auto can be less prescise and can lead to over/underexposure especially if you don't have a good grasp of your metering modes and how they work. The upside is it can be a lot faster to work with in dynamic situations where if you have a good understanding of how your camera uses metering to set exposure. A lot of use use auto ISO with an appropriate metering mode and manual exposure as another semi automatic setting (ISO priority).
I shoot with a 7D and keep mine on expanded ISO range in my settings, as either I have time to set the ISO manually (always my preference) or I'm shooting with constraints on DOF and shutter speed in a dynamic situation. Think either sports or wildlife where I need a good DOF to cover subject movement and a fast shutter speed to stop blur in changing light conditions so I cant set my ISO to one setting.