Why is it essential?

Prevent problems

Even a few minute break in website availability can cause a serious losses to its owner.
An unavailable website can mean that:

• potential buyers will choose to spend their money on your competitor's product
• users won't be able to register in your database
• your customers won't get their support
• journalists and bloggers looking for information about your company will be disappointed
• job candidates won't be able to send their CVs
• thousands of banner impressions will be lost
• Googlebot will be unable to scan the content which can possibly lower your websites's PageRank.

As the owner or administrator of the website you should always be the first person to know about a downtime. You should be able to react instantly, before your customers notice any problem.