Suppose the GUI applications are not given names in its GUI, so you don't know what to check in 'ps -A', i.e. the nameless applications in the task bar. How do I know which GUI application belong to what process and start debugging its errors (i.e. GUI frozen, program crash...)? With CLI applications, I can use attach the process to GDB and start investigating it.
To search for a specific PID i would invoke
This approach assumes that the window in question is at least a child of a process that you are aware of.