How do you choose your books for read a loud? What are your objectives for read a loud? Are you more interested in aesthetic reactions to the book or cognitive processing. These are things I wonder about when a teacher reads to a class.
In kindergarten, it is sometimes used as the introduction to a topic, as a time-filler, or as an after recess calmer-downer.
There is a lot of research out there about the influence of the read a loud. Have you given it much thought?