I have never been able to just take what they give me when I have done this on-line, and that line takes just as much time as the general line most of the time because there is often only 1 person for that line while many CMs are checking in guests in the regular lines.
In my experience, it has cost us time when we have done this, so we stopped. On our trip last week, a CM tried to check us in using her iPad. What a disaster. Complete waste of our time - had to redo everything later.
These new "time saving" things have not saved us any time when checking in.