As Starr.C wrote. You do not need the iPod Photo Cache folder, if you no longer sync with iTunes.
It has been described in this Apple Support Document (HT203156), that seems to have been removed by Apple. I can only find it on the Way Back Machine: https://web.archive.org/web/20151222081002/https://support.apple.com/en-us/HT203156
If you need to free up space on your hard drive, you can remove the iPod Photo Cache folder. Deleting this folder won't remove the original images from your library, and the folder will be recreated the next time you sync photos with your iPhone, iPad, or iPod.
The location of this folder depends on the syncing options you select in iTunes. In iTunes, if you change the selection in the Sync Photos From menu, a new iPod Photo Cache folder will be created (and the previous folder will remain).
Photos, iPhoto, or Aperture
If you're syncing from a Photos, iPhoto, or Aperture library, use the steps below to find the iPod Photo Cache folder in its default location:
From Finder, choose Go > Home from the menu bar at the top of your computer screen. If you moved your Photos Library, iPhoto Library, or Aperture Library to a different location, go to that location instead.
Open the Pictures folder and locate the Photos Library, iPhoto Library, or Aperture Library file.
Control- or right-click the file, and then choose Show Package Contents from the pop-up menu.
In the window that opens, click on and drag the iPod Photo Cache folder to the Trash.
Don't remove or modify any other file within the library package. Removing or modifying other files might cause data loss.
Close the window.
@ Starr.C: Do you perhaps know a link to an updated version of HT203156? That would be very useful to have.