The sequencer can be a real machine or a virtual machine; commonly, virtual machines are used for the following reasons:-

• They can be reverted back to a known consistent state via undo or simple file copy routines.
• They can be manipulated via scripts and have their content changed remotely
• You can run multiple simultaneous copies on the same machine, or on dispersed host machines.
• They can be created and destroyed with a very fast turn-around

There are times however when a real computer is required; for example:-

• A specific piece of hardware is required, for example a fax card, USB device, or graphics sub-system.

If you have concerns over the performance of a virtual machine, see my items on performance, specifically on processor count.