Sandboxed testing environments help review UI changes or functionality changes, providing teams with the ability to test features in parallel without blocking static testing environments. They enable dynamic creation of environments that cover various combinations of feature flags and microservice versions, allowing for efficient testing and gathering feedback from different user groups. However, managing these environments can be complex due to resource utilization and cost considerations, requiring tools like Humanitec or infrastructure-as-a-service setups to streamline workflows and optimize costs.