Good candidates include Promotion Coverage, Advertising, Distribution, and Manufacturing. Creating a combined Product-Market dimension exclusively around retail sales would make some of these other processes impossible to express. The point of this Design Tip is to encourage you to visualize the relationship between the entities you choose as dimensions. When entities have a fixed, time-invariant strongly correlated relationship, they should be modeled as a single dimension. In most other cases, your design will be simpler and smaller when you separate the entities into two dimensions.
Fact tables are incredibly efficient.
They contain only dimension keys and measurements. They contain only the combinations of dimensions that occur in a particular process. So when you want to represent the correlation between dimensions, remember that the fact table was created exactly for this purpose.