Used them last week through T2 on a ATL-LGA flight. I was in F and with the Premium line being very separate from SKY and the other Zones, it meant for minimal swimming through the crowd once we were allowed to board. To the staffing part, there were at least 2 gate agents, if not 3, present during boarding. On that specific flight, (one sample out of a ton) doesn't seem like there was a huge benefit to DL other than a bit of a better customer experience because the zone signs were utilized. Don't know that the e-gates made a big difference.