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If you don't apply the android application plugin in those modules, no

Then what would be the motive behind apply this to a root-level build.gradle file ?

to ensure they're loaded in the root project's buildscript classpath, which is inherited by all subprojects' buildscript classpaths

you don't need to set the version in each submodule

You could do something similar by using the pluginManagement block in your settings.gradle file https://docs.gradle.org/current/userguide/plugins.html#sec:plugin_management

Only about the version. Not about having it in the root build script class loader.