There are two types of market research. The first is environmental scanning. This is an ongoing process as part of the marketing conversation. Feedback is always important to make sure you are aware of what is going on.
The second type is used to validate your hypothesis before building a new product. This involves secondary research (what has been written) and primary research (talking to people). When I was teaching graduate students, the question was "How much is enough?' Which is important to know.
Research leads to planning, which leads to execution. But marketing research is time sensitive. It grows stale quickly. Not enough understanding, you do stupid things. Too much research, you miss the market window.
The risk factor determines the amount of research needed. If you have a lot of flexibility in your design, you just need to know which way the wind is blowing and you can adjust as you get into the market. Sometimes that is hard to figure. There is also the law of diminishing returns. At some point, your results will keep repeating. Nothing new is being learned.
When this happens, stop. Start executing. But always have your key one or two assumptions front and center and keep an eye out on those market conditions. Just think of the auto companies building SUVs. And gas prices of $3.