Why is Sharp plugin used?

[bsgreenb]

https://github.com/contentful-userland/gatsby-contentful-starter/blob/master/gatsby-config.js

But from the sharp docs:

By default, the gatsby-source-contentful plugin creates a ContentfulAsset node for every image with links to Contentful’s CDN, therefore it is not necessary to use gatsby-transformer-sharp together with gatsby-source-contentful.