Webp is superior to jpg and far smaller than png. Making a map tile that has transparency and is bigger than 20x20 grid squares leaves you the choice between a huge png or a tiny webp. VTTs like foundry have best practice guidelines re image sizes and formats and it is simply not possible to follow these using png unless the map in question is tiny, and if you ignore them and just go for a huge png your players may be faced with lag, longer loading times etc.