A forecast without an error range is a guess
A forecast without an error range is a guess with a decimal point. The useful question is not "what will demand be" but "how wrong might this be, and what does that cost me".
We build models that answer both, evaluated against how well your current method does — which for demand planning is often a seasonal average that is harder to beat than people expect. When we beat it we can say by how much; when we do not, you have saved the build cost.