* Can run headless and detached from GUI
* can teleport VMs between hosts, even if they run different OSs
* free and easy to install/use.
I don't find that VMware workstation is any better in general. VMware can run virtualize ESXi easily and work as in interface to a full ESXi though.
KVM with Virt-Manager is comparable to VirtualBox IMO. It can be extended with oVirt and OpenStack. It's Linux only which hurts it for desktop, but not servers.
In general, if you need something quick on your desktop, VirtualBox is great. As you get into details, different hypervisors offer different advantages.