Delete photo after importing to iMac

Even if "delete after Import" is there, do not use it. Quite a few users lost their photos because of it.

The problem is, that the photos will be erased from your iPhone, before you can check, if the import has been completed correctly. In rare occasions, the Mac could crash, before the imported photos have been saved in your Photos Library, but have already been deleted from the iPhone. Or the photos may have been imported with transmission errors and the image files are damaged and useless. And when you notice it, the files have already been deleted from the iPhone.

It is much safer to wait until you have made the first backup of the imported photos, and then use Image Capture to delete the photos from the iPhone.

It's not there if you're syncing with the iCloud Photo Library.