Entrepreneurs are optimistic by nature, and every financial forecast I see shows a shiny company company after 5 years with huge sales, profits, and cash flows. Nobody believes the forecast anyway, and it cannot possibly be accurate, but still, the 5 year revenue and profit scenario serves a purpose.
It enables the investor to think "what do I have to believe" in order for this to become reality. There is the sanity check on the revenue side, that I have written about before, but the cost side is actually equally important.
Yes, a company with big sales will probably have big profits. But it is good to go beyond the basics. A sensible cost structure shows the investor that you understand the business you are operating in. If you aspire to become a global software company, your economics are likely to look like that of other global software companies. $200m in sales and $190m in profits don't usually work.
A financial forecast also guides your operating plan. If you need to convince 30 enterprise customers per month to sign up, each requiring a 6 months sales cycle with 5 on site visits, you can work out what sort of sales force you need. Sales costs are no longer "30% of revenue", but you can make a more informed forecast.
So the point estimates of the 5 year forecast are not that important, it is the logic that went into them that is.