What is the recommended approach to estimate the scale of changes required for mobile optimization?

The recommended approach is to conduct an SEO audit focusing on both mobile and desktop optimizations because mobile optimization is not an isolated task; it's part of a holistic SEO strategy. Understanding the current state of both mobile and desktop performance provides a comprehensive view of the website's strengths and weaknesses, allowing for a more accurate estimation of the required changes and their potential impact across all user experiences. Analyzing only mobile traffic in a testing tool or desktop traffic in Google Analytics provides an incomplete picture, potentially leading to misprioritized efforts or overlooking critical interdependencies between mobile and desktop experiences. An audit focused solely on mobile might miss foundational issues on the desktop site that also affect mobile performance.