Simply put, a pipeline asset plugin replaces a resource plugin and should be used to manage your assets (such as js and css).
The resource plugin existed before the pipeline plugin. It was used to facilitate and standardize the use of assets in the Grails application. It was later replaced by a plugin for connecting to resources.
The plugin for connecting to resources is a very capable, multifunctional and extensible plugin for managing your assets (mainly js, css). It also has several other additional plugins that allow you to pre-process assets (e.g. LESS).
While using the plugin for the pipeline does not match recommended and default for later versions of Grails.
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