The author uses the terms "data dumps" and "garbage disposal" on pages two and three to suggest that dreams are a way for the brain to get rid of unnecessary information.
This is supported by the theory that dreams serve as a way to clear the brain's short-term memory. When we sleep, the hippocampus, which is the part of the brain responsible for short-term memory, uploads its contents to the neocortex, which is the part of the brain responsible for consciousness.
So, The author's use of the terms "data dumps" and "garbage disposal" suggests that the hippocampus is simply getting rid of information that it doesn't need anymore. This is similar to how we might use a garbage disposal to get rid of food scraps that we don't want.