Google Compute Engine allows for you to change the machine type of an instance as described here:
In Terra, if I stop my notebook VM and change the configuration, my existing instance gets destroyed.
Similarly, Google Compute Engine allows for you to increase the size of a persistent disk as described here:
In Terra, I don't have an option of increasing the size of the PD.
This means that I end up needing to reinstall libraries and tools on my VM, and so I might instead decide to just plug along. We lose a great piece of GCE functionality here.