Which practices should be avoided in classical ABAP programming?

Fetching all data from external networks should be avoided in classical ABAP programming due to several important reasons related to performance and resource management. When you fetch all data from external networks, it can place an excessive load on both the network and the application server, especially if the volume of data is large. This practice can lead to increased response times, potential timeouts, and a heavy impact on network bandwidth, making the application slower and less efficient.

Instead of trying to retrieve all data at once, it's generally better to implement data pagination, filtering, or fetching only the necessary data to ensure that the application is responsive and efficient. This aligns with best practices in programming which emphasize working with only the required data segments to optimize performance and resource utilization.

In contrast, minimizing database load, controlling data fetch on the application server, and employing parallel processing of data are practices that enhance performance. They ensure that network and server resources are utilized efficiently, leading to a more responsive application.