Monitoring from multiple monitoring zones allows you to monitor the experience of customers from many locations, which is important for companies that do business in more than one region. Consider this: your website might be working fine in the Western United States, but users from the Eastern half of the country are experiencing high load times and nonresponsive web pages. Monitoring from just a western datacenter would report an OK status, but if you also monitor from the eastern datacenter, you will be alerted to this problem before it affects your customers.
If you're only monitoring from a single zone, and for some reason there is an error with a check, you may get false notifications that your site has a problem, when in reality it is working fine. Using multiple monitoring zones helps prevent these false alarms by verifying a system failure from multiple sources before alerting you. Or, you can have it send you a message if even just one check returns a failure status - the level of customization possible through our alarm language is incredible.