Explain please...Based on the book below, chapter 14 (Short-Term Financial Planning)...There are about forecasting financial variable....can you explain the note below....i don't understand it.

GLOBAL EDITION Foundations of Finance The Logic and Practice of Financial Management TENTH EDITION Arthur J. Keown John D. Martin J. William Petty Chapter 14 Short-Term Financial Planning Forecasting Financial Variables Traditional financial forecasting takes the sales forecast as a given and projects its impact on the firm's various expenses, assets, and liabilities. Most common method used for making these projections is the percent of sales method