TIB: I've been on a couple of track days where warmers are only allowed in the top couple of groups to try and encourage people taking it seriously to select a different group to people doing their first day. I don't think it was enforced particularly, just to help people select the group appropriate to them.
Fallout: Unless you're going to get some proper lean on into the first corner you'll probably find for the first part of the day you take longer to warm up mentally than the tyres take to get sticky. By the afternoon just be a bit respectful for 2-3 laps depending on the circuit and build pace. It's not bad advice anyway really
Jambo