Defining the needs of buyers in ever-narrowing niches is not the same as identifying new markets. The latter often requires de-segmentation by defining key commonalities across buyer groups. This creates differences in strategies and tactics.
Here is an example of applying this to book marketing. When selling my book, Job-Search 101, I initially sought to define niches -- graduating college students, high-school students, blue-collar workers, unemployed people who were 55 or more in age – and tried to sell to them with different approaches. But the common element across all these niches was that people wanted a secure future and a source of that security as quickly as possible. I changed my promotional strategy to address this subtle difference increased my sales, revenue and profits.