I find theres 2 schools of thought Scott - By the book or by the individual - If you go by the book, ALL artexed ceilings should be overboarded to erradicate any possibility of the new plaster bringing the whole ceiling down - In practise, I should imagine 99% of us will either use a tight coat of bonding and then skim, or just skim with 2 decent coats of PVA
I have been guilty of overboarding a lath and plaster ceiling, but only because I was confident it was fairly sturdy and I was also using 50mm screws into the joists - Again, going by the book, you should never overboard L&P ceilings, but have you ever seen the mess made when you take one down ? The homeowner will be hoovering up dust for weeks !!
In short, I'll only overboard if I'm unhappy with the integrity of the ceiling - Ie, patchy artex is always an alarm bell ringer, as is large water damaged areas and very rarely will I rip a ceiling down because I've then got to dispose of it !!