Can someone explain VPS to me?

 
What is it?  When is it important?  
 
wikipedia:
A virtual private server (VPS) is a virtual machine sold as a service by an Internet hosting service. A VPS runs its own copy of an operating system, and customers may have superuser-level access to that operating system instance, so they can install almost any software that runs on that OS.
MetaQuotes offer an alternative to traditional VPS - tutorial here 
Reason: