In the latest release there were added the possibility to also poweroff a VM instead of just suspend (savestate) it.

Poweroff is fine, if you've made the root disk reverting back to orig state on poweroff (or sometimes have to recover your machine from a snapshot if the filesystems were corrupted by the hard poweroff).

But it would be better to be able to shutdown VMs in a clean way -> send ACPI Poweroff event to the VM, so the kernel can shut down (acpid does this on Linux, on Windows it depends on your energy settings what the poweroff button does).

There should be at least all options to stop the slave that the API offers: https://www.virtualbox.org/sdkref/interface_i_console.html

Or vboxmanage:

VBoxManage controlvm        <uuid>|<name>
                            pause|resume|reset|poweroff|savestate|
                            acpipowerbutton|acpisleepbutton