Here's an article from the ever interesting Nielsen Norman Group—Ideation is for Chumps.
It's an April Fool, but in some cases is scarily accurate.
In my experience, ideation can be dismissed as a waste of time. I've seen people become frustrated and impatient about what they perceive to be a lack of progress—especially so when you write off new ideas and return to previous ones. But in almost all cases when someone creates a design and wants to move forward without any process of ideation, the results are bad. Use cases are usually lacking. Dependencies with other features may not be thoroughly explored. The design is probably a derivative of pre-existing solutions that don't necessarily address the root of the problem being solved. If you step back through the process for a feature that is not performing as well as it should, a lack of ideation is usually apparent.
My experience shows a correlation between successful products and features—things which people love and find easy to use—and a process that values ideation, experimentation, and iteration.