Can my Mac and my iPhone save to the same destination?

Yes. Parachute Backup for Mac and for iPhone and iPad write the same folder structure and the same file names, so each app recognizes what the other already copied. Your originals are written only once.

For iCloud Drive and other folders, sharing works with some limits, so it is simplest to let one device take care of them. One more thing to expect: viewing an edited photo at full size updates the date of its edited version on that device only, so that file may be copied again now and then. It costs a little time, not data.

This is for one person with several devices. If two people with different Apple Accounts use Parachute Backup, give each of them their own destination folder.