The regular “Smart” and “Rotation” modes sort items by their last schedule date (oldest to newest), so that items whicih haven’t been scheduled for a long time will get scheduled first.
“Advanced Rotation” allows you to specify different sort criteria, e.g. the item ID, title or filename.
It will also store the index of the last scheduled item internally, so it will resume where it left off when you schedule for the next time. (Doesn’t work if you re-generate hours.)
You are correct in assuming that this was initially implemented for a customer. That particular customer has a folder full of items (spoken text, in that case) which he wanted to schedule in the correct (alphabetical/numerical) order, one by one, at a particular time each day. Think audio book episodes.
By the way, I released 7.4.0 as stable now.