Intel VT-x is a set of processor enhancements to improve virtualization performance. In theory, VT-x should allow for near-native speed in a virtual machine. VirtualBox, a popular open source virtualization program, recently added a check box to turn on VT-x or AMD’s AMD-V equivalent. But VirtualBox’s site warns that enabling it may reduce the performance of a virtual machine:
However, we do not make use of these features by default. The reason is very simple: our x86 virtualization is very sophisticated and in most cases it provides significantly better performance than when relying on VT-x. Virtualization products that rely on VT-x are usually much less sophisticated and tuned.
They say there is one benefit to using VT-x, reliability: