My experience with Research and Personas, at least the way the marketing folks talk about, is that it's been pretty useless.

I really think the distinction between "user needs" they make using Demographic, Behavioral or zillion other types of segmentation doesn't really add much value to product design, unless you are building something for a very narrow audience (For instance an enterprise product for a specific department in a specific industry/company).

The other thing that I have found completely redundant is "asking users what they need". I think as designers we must observe our audience using our or competitive products and use empathy to discover ways to solve problems that even the users don't know exist. For that reason I have not found much value in involving the users right through the design and development process, because they are not able to articulate how the dots connect by looking at a structure, sitemap or wireframes.

Designer, Growth Marketer & Product Leader