WebP was designed for the web. Its lossy mode generally reaches the same visual quality as JPG with fewer bytes, it supports transparency, and current versions of Chrome, Edge, Firefox and Safari display it. Smaller images mean less data to download, which matters most on mobile connections.
Google's WebP documentation describes its lossy files as typically 25 to 34% smaller than comparable JPGs. Real savings vary from image to image, so compare the before and after sizes the tool shows for your own files.