Delete removes it from your device and the online version (via the bin for a while). That frees up space on both and also allows you to erase the evidence.
Delete device original keeps the online copy so only frees up space on your device.
Thanks - opposite of what I want: delete the Google photo and keep the original on my device. I thought I previously had instructed Google not to make copies of any photos or videos that I had taken, maybe an update erased that preference?
Delete removes it from your device and the online version (via the bin for a while). That frees up space on both and also allows you to erase the evidence.
Delete device original keeps the online copy so only frees up space on your device.
(AIUI)