1. Rendering Issues: Different email clients interpret HTML and CSS differently. If your code is not clean and standardized, your email may not render correctly across all clients. 2. Increased Load Times: Poorly written code can slow down the loading time of your emails, frustrating recipients and leading to lower click-through rates. 3. Security Vulnerabilities: Neglected code can become a security risk, making it easier for malicious actors to exploit vulnerabilities. 4. Maintainability: Untidy code is difficult to update or modify. This can make it challenging to make quick changes or troubleshoot issues, leading to inefficiencies.