The recommended approach for preventing users in the "user_group1" role from using gaming and peer-to-peer applications in an ArubaOS environment is to enable Deep Packet Inspection (DPI) and add application rules that specifically deny access to these types of applications for the role. DPI allows the network system to analyze the content of network traffic in real time and apply policies based on what it detects, including blocking specific applications like gaming and peer-to-peer sharing. This capability is essential for effectively managing application usage on the network and ensuring compliance with organizational policies. Application-specific rules provide precise control over the network traffic by identifying the application regardless of the network port used, making it a more effective method than blocking based on ports or IP addresses.