Website monitoring services are essential to large websites that are profit-motivated. As the name suggests, they monitor the website for downtime, broken links, faulty code, incompatibility, and a variety of other maladies that affect website operation. Depending upon the level of services provided by the monitoring service, they could just send a report to you detailing the downtime and problems with the site. Some will test the website thoroughly, send you a report, and have someone fix the problem for you immediately. It all depends on what you're willing to pay for.