Converting JPG to PNG gives you a lossless file you can edit and save again without the extra quality loss that JPG adds every time it is re-encoded. It is also the quickest way to satisfy an app, template or upload form that only accepts PNG.
Be realistic about what it does. A JPG has already thrown away detail, and converting to PNG cannot bring it back: blocky artefacts and soft edges are preserved exactly as they are. It does not create transparency either, because the JPG never had any. Expect the PNG to be several times larger than the original, particularly for photographs. If the goal is a smaller file, WebP is a better target.
PNG is lossless, so the quality setting does not apply to this conversion. Pixel dimensions stay the same, each file keeps its name with only the extension changed, and nothing is added to the output. Camera metadata such as EXIF is not copied across. All processing happens in your browser.
When it is worth doing: use PNG when you will keep editing and saving the image, when you need a lossless source for graphics work, or when a tool simply will not accept JPG. For sharing or publishing photographs, the original JPG is almost always the better file.
No. PNG stores the pixels exactly as they are, including any compression artefacts already in the JPG. The benefit is that further edits and saves will not lose more quality.
PNG keeps every pixel without discarding detail, while JPG compresses photographs by discarding what the eye is least likely to notice. For photos the PNG is often several times larger.
Not with a format conversion. JPG has no transparency to preserve, so you need a background removal tool to cut out the subject.
No. The converted file contains only the image, so camera details and GPS location in the JPG are not copied.
No. Everything runs locally in your browser.