A mono repository organizes multiple Terraform configurations as separate directories within a single repository, while a multi-repo approach uses separate repositories for each configuration. Mono repos are suitable for small projects or teams with uniform access to infrastructure configurations, but can lead to increased module maintenance overhead and debugging complexity. In contrast, multi-repos offer better granular access control and configuration changes, making them ideal for large teams with complex infrastructure systems. By separating configurations into individual repositories, teams can self-service and compose based on shared building blocks, allowing for independent testing of modules and optimized continuous integration pipelines. However, this approach may result in slower Terraform initialization times due to the need to download remote modules. Ultimately, the choice between mono and multi-repos depends on the organization's specific needs and patterns.