While some technologies for web development have changed rapidly -- the rise of Node.js based IDEs, for instance -- others have remained stationary. The use of image formats has been static for decades, with the largest shift being from GIF to PNG (and arguably H.264 for animated content). That doesn't mean there aren't options vying for market share, with Google's WebP being one contender.
Adrian James and Matt Shull over at Smashing Magazine have put an interesting case together for adopting WebP for future web development. The biggest pro is the 20-25 per cent reduction in file sizes on average compared to PNG and JPEG. There's also consolidated support for features such as transparency and lossy / lossless compression, which are mandatory for building any site.
Unfortunately, these benefits are small consolation if your Edge, Safari and Firefox users (not to mention the plethora of other browsers there) can't see them. Even after half a decade, it's hard to argue for WebP.
Eventually we'll see more efficient image formats grace the web, it's just going to take longer than it has for audio and video.
Guide To Using WebP Images Today: A Case Study [Smashing Magazine]