Deploying the SD-WAN controller on-premises offers several advantages, particularly in terms of control and customization.

Full Control of the Data Plane and the Control Plane: When the controller is deployed on-premises, the organization maintains complete control over both the data plane (traffic forwarding) and the control plane (network management and configuration). This allows for more granular control over network policies, security configurations, and performance optimizations.

Customization and Security: On-premises deployment allows organizations to customize their SD-WAN setup to meet specific security and compliance requirements. Sensitive data remains within the organization's control, which can be crucial for industries with strict data privacy regulations.

Operational Flexibility: Having the controller on-premises provides operational flexibility, enabling organizations to integrate the SD-WAN solution with existing network management tools and processes.

Cisco SD-WAN Deployment Guide

Cisco SD-WAN On-Premises Controller Configuration Documentation