Starting with SQL Server 2008 the product supports the ability to start using or stop using CPUs that are dynamically added or removed to a running system, either physically, logically (by online hardware partitioning), or virtually through a virtualization layer.
Only the Enterprise Edition (or a Developer Edition or an Evaluation Edition, both of which behave exactly like the Enterprise does. The only difference among them three is their licensing.) gives the DBA the flexibility to dynamically resource more or less CPUs to SQL Server as the need fluctuates through this hot add CPU feature.
This post is part of the a series I decided to call “Understanding the value of the Enterprise Edition, one feature at a time” which I started in September 2011 and will grow on a weekly basis, having a new post incorporated to the family every Friday.