I think a roadmap is important at every stage. Now, keep in mind that I don’t think of a roadmap as a list of features to be built. In no way is it a commitment. Instead, think of it as a way to outline and check your assumptions about the obstacles your business will face, and how you might tackle them. In this way, your roadmap is more of a prototype for your strategy - not something that perfectly captures the final plan, but instead a device to help communicate where you are now, where you hope to get to, and what problems you will need to solve along the way.
If the rest of the team understands the problems on the horizon and there’s an agreed strategy on what order you’ll tackle them, it means everyone can pitch in to help take down each challenge as they come up. Having a roadmap hugely empowers your team, whether large or small.