I can confirm that the CleanWebpackPlugin has zero impact on deploy time. I was using it when the builds were 45 minutes.

There's a bunch of optimizations that goes into the webpack splitChunk plugin and it's actually one of the recommended way to speed up webpack compile time. Here are some references:

https://webpack.js.org/guides/build-performance/#smaller--faster

https://medium.com/dailyjs/webpack-4-splitchunks-plugin-d9fbbe091fd0

https://dev.to/paulcodes/web-performance-case-study-webpack-splitchunks-3ek3

My guess is that it's because of a combination of these factors:

* reduced bundle sizes

* if you have a o(n2) operation on one big file it's slower than the same o(n2) operation on many small files (and maybe filter out file that don't need the operation)

* usage of async import in the code seams to filter out some unnecessary bundling

Like you, I would love to have a deeper understanding of what is actually happening here. However, I just try to get over as fast as possible with devops and put my time on features that actually matter to the customer XD. By the time I master webpack, something new will have come out and I won't need this knowledge anymore.

Best,

Phil