Sandboxes should be refreshed based on the needs of the project and the development lifecycle. Production is the only pristine environment, so it is a good practice to refresh sandboxes from production regularly to ensure data and metadata consistency. Integration sandboxes should be refreshed frequently, not rarely, to avoid conflicts and errors when integrating code from multiple developers. Development environments should generally be refreshed after each working feature has been successfully migrated, to avoid accumulating unnecessary changes and to start fresh for the next feature.