A load balancer in network architecture serves to distribute incoming traffic across multiple servers to ensure optimal resource utilization and enhance availability. By managing network traffic, it helps to prevent any one server from becoming overwhelmed, thus maintaining performance and reducing downtime. Load balancers can be hardware-based or software-based and support various algorithms to determine how requests are distributed. This technology is critical for scalable applications, as it ensures that user requests are handled efficiently and delivers a better overall user experience.