The function of a load balancer in software architecture is to distribute incoming network traffic across multiple servers to ensure optimal resource utilization and application reliability. By balancing the load, it prevents any single server from becoming overwhelmed, thereby enhancing system performance and minimizing downtime. Load balancers can operate at various layers of the OSI model, using algorithms like round-robin or least connections to determine how to direct traffic. This mechanism not only improves response times but also enables seamless scaling of applications, ensuring they remain responsive under varying levels of user demand.