JPEG is argumentatively the most popular image formats uses for digital photography. It is so because compression they use which results in an impressive reduction of file size which makes it appropriate where size matters particularly where storage media is costly or small like in the case of digital cameras and for the use on the internet where bandwidth may be slow or costly. Now that we are in the age where speed is everything, waiting too long for a web page to download because of huge image may cause your visitors to move away to somewhere else.
Of course now, professional digital cameras do offer saving photos in the RAW format but that would result in about 10x the space needed to store a typical jpeg photo. RAW format has its purpose where quality is everything.