The best approach for streamlining job configuration for multiple similar projects is to use Pipeline as Code. This allows the administrator to define job configurations in code, enabling version control and easier management.

Regularly backing up Jenkins is a key practice for beginners to ensure efficient use. It safeguards configurations, job settings, and other critical data.

Configuring Jenkins Failover ensures seamless job execution in a high-availability setup. If one Jenkins instance fails, another instance takes over to maintain continuous operation.

Jenkins achieves high availability by employing load balancing techniques and distributing master nodes to ensure continuous service even in the face of node failures.

The REST API in Jenkins primarily uses JSON format for job definitions. This format is widely used for its simplicity and ease of parsing, making it suitable for automated job creation.

Automated testing in Jenkins is typically configured in the 'post' section of the pipeline script. This section allows you to define actions that should be taken after the pipeline's main execution, such as running tests.

Implementing Distributed Builds is critical for optimization when managing hundreds of jobs in a Jenkins setup. Distributing build tasks across multiple agents helps distribute the workload efficiently.

In a large-scale setup, Load Balancing is crucial for maintaining an efficient build process. Load balancing distributes build jobs across multiple build agents, ensuring optimal resource utilization and faster build times.

The Downstream/Upstream Projects feature in Jenkins is used to manage job dependencies in a complex workflow. It allows one job to trigger the execution of downstream jobs based on the completion of the upstream job.

The Input Step in Jenkins pipelines allows dynamic parameters based on user input, providing flexibility in pipeline execution based on user choices.