Before you dismiss it for being too simple, think about the wider audience of startup founders, not just YC readers. They often can't predict churn rates or viral growth timelines or per-user infrastructure costs. This is a great starter model to say, "At the very minimum, you should plan on having $X."

After the first year of doing business (or faster?), you should revisit your model with these kinds of metrics and hone the model, but you usually won't have it going into year 1.