Test the concept from the start: The first advantage is that you will be able to consult your market, to see whether or not it is receptive to your project. And this before you even design anything, since you only need your ideas to create the questionnaire.
Validate your targeting: You can directly question your target market, and identify your best prospects. Are your assumptions about your ideal customers correct? Is there a more interested segment? Ask the right questions, and identify the most interested profiles.
Test a need, identify expectations: Is the problem you want to solve real? What frustrations does this generate in your prospects? What are their specific needs?