The main advantage of custom website development is that clients can have unique websites that are tailored to their business-specific needs. Other advantages that website owners can leverage through customization are high performance, robust security, scalability, better user experience, SEO-friendly site, and seamless third-party tool integration. However, there are a few disadvantages of custom website development, like high development costs, time-consuming, lack of control, challenges while integrating third-party tools, data breach risks, and dependency on service vendors for updates or changes.