virtualbox.org

> you can change the default location
I want the default location to be the host's C:\ drive. But when it starts getting filled I move the older VDIs to another drive.

A VDI copy is not a backup of the VM and hence is not an answer to the original query.

I don't understand what it is that you want: you already know how to copy the entire VM folder, that is a complete backup and you may then delete the original VM if you want to recover the space. The procedure is identical to that described in the FAQ: Howto: Move a VM.

If I am creating a new VM to work with I want it created on the host.