V2EnabledWithHelpers just registers dummy DGPv1 tasks/configurations so that build scripts can still be compiled. It just helps make it easier to migrate to v2.
For example, if you have a build script that references v1 tasks or configurations and you update DGP to v2 immediately then Gradle will no longer be able to compile the build script, so you get a bunch of compilation errors and lose IDE features, making it harder to migrate.
The name 'with helpers' is perhaps misleading. It's purposefully vague because we might add more migration tools if there's a good use case.