Hiring a Cross-Browser Developer is crucial for ensuring that your website or web application functions flawlessly across different web browsers. They have expertise in addressing compatibility issues between various browsers like Chrome, Firefox, Safari, and Internet Explorer. This professional can make your product accessible to a wider audience, improve user experience, and consequently, increase user engagement and conversion rate. Their knowledge in HTML, CSS, JavaScript, and testing tools can help in spotting and fixing inconsistencies, thereby maintaining your website's performance and appearance across all platforms.