When PNG to JPG is the right move
PNG is the right choice when an image has sharp edges, text, or transparency: logos, icons, UI screenshots, technical diagrams. JPG is the right choice when an image is a natural photograph: people, landscapes, products, food.
If you have a photograph saved as PNG, you are paying a 5–10x file size penalty for no visible benefit. Converting to JPG is the single most effective way to make the file dramatically smaller while keeping the image looking the same.