Conversion Rate Optimization (CRO) is crucial for online businesses as it focuses on maximizing the effectiveness of existing site traffic, rather than just increasing visitor numbers. By improving the user experience and streamlining the conversion process, CRO enhances the likelihood of visitors completing desired actions, such as purchases or sign-ups. This leads to a higher return on investment from marketing efforts and can significantly boost a business's revenue without the need for additional traffic. Effective CRO strategies ensure that every visitor to your site has the best chance of converting, making your marketing and advertising efforts more efficient and cost-effective.