This depends on the situtation. Especially when writing something that doesn't have a good existing pattern (think research code). After writing something it mi

This depends on the situtation. Especially when writing something that doesn't have a good existing pattern (think research code). After writing something it might become clear that a everything would be better off one way or another, and adding new research features might be impossible given the current structure. This is why most packages for doing machine learning research have just turned into autograd tools. Picking any fixed structure for research code is effectively blocking off some avenue of research.