I had the same experience Friday on DTW-IND. Small bags were specifically bags which would fit under the seat in front of you. The gate agent was pretty rude about it and seemed as frustrated as everyone waiting to board and was arguing what would and would not fit under the seat.

All in all, I don't think it impacted boarding significantly, but nobody had to check a bag, so maybe it worked. I had a carry on, so I didn't get to see if they were enforcing passengers with bags which will fit under the seat actually be put under the seat during the early boarding, but I was able to stow my roller bag and briefcase in the OH, so I was happy.