Many modern Rails application use third-party assets like JavaScript and CSS libraries or frameworks. In most cases these assets are minified and compressed by tools outside of the Rails asset pipeline. For example popular gem React on Rails uses WebPack to build JavaScript bundles. When we include these files to assets pipeline it goes to minify again. We can safely avoid double minification and reduce assets compilation time. Meanwhile it is still good to add a digest and gzip compression.
Savings are strongly depend on how many minified assets are used in an application, some numbers for a random application:
# standard setup