Whether we are talking about a highly available and critically productive environment or not, any planned or unexpected downtime means financial losses. Historically, solutions that could provide high availability and redundancy were costly and complex.
With the virtualization technologies available today, it becomes easier to provide higher levels of availability for environments where they are needed. With VMware products, and vSphere in particular, it's possible to do the following things:
Have higher availability that is independent of hardware, operating systems, or applications
Choose a planned downtime for many maintenance tasks, and shorten or eliminate them
Provide automatic recovery in case of failure