Sources:

• https://wpmudev.com/blog/wordpress-image-sizes/
• https://kb.hrcws.nl/change-or-stop-divi-image-size-thumbnail-generation/

When you upload an image to WordPress, the system keeps the original file as is and generates several additional file sizes:

• Use a plugin like Imsanity to reduce the size of the originally uploaded image and save disk space.
• WordPress generates 3 additional file sizes as specified in WP admin » Settings » Media.
• Your theme can generate additional file sizes.
• Plugins can generate additional file sizes.

My preferred settings to reduce the number of additional image files that are generated:

• Imsanity
  • 1920×1920 or 1536×1500 (1536 is a Divi size)
• WP admin » Settings » Media
  • Thumbnail size: 300×300 (Divi size)
  • Medium size: 1280×1280 (Divi sizes)
  • Large size: 1920×1920* or 1536×1500 (same as Imsanity)