Modern high-traffic websites must server many concurrent requests from users, and they are expected to reply in a fast and reliable manner.
A load balancer is sitting in front of the servers and dispatch the requests across all servers in order to maximize speed and to ensure that no server is overworked, for performance-related issues.
In case a server goes down, the traffic is redirected to other online servers.
In case a new server goes up, the load balancer automatically starts sending requests to it.
Load balancing is required to service requests in a manner that maximizes speed, capacity utilization, and it makes sure that no server is overloaded with requests.
The load balancer also redirects requests to the remaining host servers if a server goes down.