Reasons for making this change:

Terragrunt is a thin wrapper tool for Terraform: https://terragrunt.gruntwork.io/

It makes sense to add this to the Terraform template, because if one is using Terragrunt, then by default Terraform is also being used. Terragrunt is popular and increasingly becoming a necessary wrapper for complex Terraform operations.

Links to documentation supporting these rule changes:

Documentation which highlights the caching folder:
https://terragrunt.gruntwork.io/docs/features/caching/#clearing-the-terragrunt-cache

The generate command which creates arbitrary generated* files in the current working directory:
https://terragrunt.gruntwork.io/docs/reference/config-blocks-and-attributes/#generate