If most users need to see the full set of joined data from two tables, collapsing the two tables into one can improve performance by eliminating the join.
For example, users frequently need to see the author name, author ID, and the blurbs copy data at the same time. The solution is to collapse the two tables into one. The data from the two tables must be in a one-to-one relationship to collapse tables.
Collapsing the tables eliminates the join, but loses the conceptual separation of the data. If some users still need access to just the pairs of data from the two tables, this access can be restored by using queries that select only the needed columns or by using views.
