"When you are updating website you need to send error 503 to client. Error 503 indicates that Apache or Lighttpd web server is temporary out of service. This is useful if you are running popular database driven community or e-commerce website. Error 503 informs search engine that site is temporary out of service. This is quite important for site which is heavily depends upon search engine for selling products and services. So when the site is under maintenance you can send user a good message indicating that site is down for some work."
