It allows multiple virtuals to run on a single computer.

It allows the running of older operating system versions on top of newer operating systems when hardware incompatibility otherwise prevents operation of these.

It can work around marginal software. For instance, the Windows Raid scheduler for SATA drives works on ticks (thousandths of a second). As a result, it cannot natively read from arrays of SSDs at a speed greater than the read rate of a single drive. But with virtualization, Windows sees only one device and thus runs at the full array speed.

Because virtual systems are atomic, they can be moved among physical systems, and can be replicated as exampled in our high availability discussion.