I_H_Yoo:

So can I say that functional is for re-use?


That is more “if you implement something new, provide both because you don’t know which is more convenient to your users”.



 I_H_Yoo:

What do ‘stuff without state’ and ‘quantization’ mean?


That’s another slide, there.
Or, try the “what is nn” tutorial 15.
Quantization has its own set of tutorials 11.


Which should I use between functional and Module?


For softmax, and if you aren’t building a  Sequential, I’d use the functional interface. But there is a modicum of taste in that.
Best regards
Thomas