I work in a library that has a waffle shaped ceiling. I asked the manager about it one day and she said that it has two purposes.
The first is similar to what was mentioned in the article. The design helps to trap pockets of heat and cuts down on energy costs.
The second is a benefit that is kind of unique to libraries. The pockets help to capture sound and prevent large noises from traveling across the whole space of the library. Its a pretty coll idea and it sure beats saying shhhh! all the time.