It is very useful for cracking. For example, you can fake cpuid and use it as break. I've used cpuid as break point to catch when application is using it for anti-dump. VT also allows you to have hooking on x64 system without disabling PatchGuard, as you can control drX registers, and hook using them. You can also hook all system calls, as you are controling read/write to MSR registers for example. (eg. ron ead you fake to real-old address, and keep yours inside)
It's also useful for virtualization software like VmWare, VirtualBox, VirtualPC as it will speedup their execution a lot
