What can go wrong if I do not know my target group?
You are dependent on your target group for reaching the goals of your project. If they don't participate, you won't be able to reach the savings you want to achieve.
It is thus important to know about your target groups' needs, motivation and competencies. You need to understand the practices that you want to change. You also need to know about the barriers to change (why aren't they already doing what you want them to do?). In order to communicate with them, you need to know who they regularly interact with, who they trust and what they expect from you and your project.
If you fail to address these questions, you might end up with a project that you like a lot, but that fails (or at least partly fails) to engage your target group.