It’s a long story, and has been covered in other threads.
In short, if you’re looking for one coherent policy answering all of these very pertinent and clear questions, you are out of luck.
The answers are contained in the responses to FOI requests which others have made having asked the same questions and received nothing from the chain of command.
The good news is, outside of the limited activities which clearly state the forms ARE needed. You don’t need them for the rest! Admin Reduction at its best.
See my topic here: TG Forms, Policy on when required?