While this is a great module and I would recommend using it if you have the possibility to do so, there are several downsides to using it out-of-the-box: first and foremost in this threads context, it does not create webp images that will be stored on the filesystem, but rather it creates them on the fly, every time a visitor needs an image resource. What this does, essentially, is lowering bandwidth requirements at the expense of increased CPU and memory usage on the server side.
Hence it is a trade-off that may or may not be worth it depending on your configuration. This is not a problem if you use my module - either standalone or in conjunction with the pagespeed module for apache/nginx, as in this case the webp images will be fetched from the filesystem instead of being recompressed on the fly - thereby lowering the bandwidth requirements and putting no additional strain on the CPU and memory resources.
Furthermore, if you are on e.g. a shared hosting and your hosting provider does not allow you to use the pagespeed module for apache/nginx, you are dead in the water.