Every FM / OO method can be considered a black box. It has inputs and outputs. Suppose that you know that people often want to do "X". "X" has steps 1 - 10. The condition of the Stack before the process are the inputs to "X" and the condition of the stack after the process is run is the outputs from "X". You can simplify this by saying that anything in the stack that can not be changed by "X" need not be included in Input or Output.
So, now you can build "X" as a static FM in SAP.
This simplifies your code creation needs by only requiring you to write a generator the call to X in order to have the created program perform "X".
Now obviously Fm's and OO Methods won't need to be "feed with assign field symbols". However you can also use remote performs in a static Include program. These could be "feed with assign field symbols".
Neal