The purpose of financially evaluating an idea before project approval is to ensure that the project is viable and worthwhile from an economic perspective. This evaluation, done during the Evaluating step of the pipeline, involves analyzing the expected cash flows and using various financial metrics to determine the project's profitability, risks, and the time needed to recover the investment. 

By conducting this evaluation early on, decision-makers can identify potential issues, compare the idea against alternative investments, and make informed decisions about whether to proceed with the project. This helps in optimizing resource allocation and avoiding investments in projects that are unlikely to yield sufficient returns.