Why convert JPG to PNG
PNG isn't usually smaller than JPG — quite the opposite. The real reason to convert is compatibility: some design tools, templates, and online forms only accept PNG files, and reject JPG outright regardless of quality or size.
There's also an editing angle: PNG is lossless, so if you're going to open, edit, and re-save an image several times, starting from PNG avoids the fresh compression artifacts that JPG adds on every re-save. Converting once to PNG before a round of edits keeps later saves clean.