If something is worth doing, it's worth evaluating. You have to make sense of it all - enough, at least, to decide what to do next. To make good decisions you have to gather the data, and group it, and analyse it, and impose value on it. What are you doing right? Where could you do better? Of the things you could do better, which is more important?
A program that is properly evaluated gives twice: first, in the impact it has, and second, in making it possible for you - and others - to do better next time.
A top-notch project evaluation is not an end in its own right. Ultimately, what makes project evaluation worthwhile is making a difference in people's lives.
For people, for programs, for organisations, data is a torch in the fog.