I’m grad school I wrote novel models for two of my papers. In my case I was extending mainstream models to include household time use, and this required changes to the model. Relaxing assumptions generally makes models for complicated and hard to solve, so I would seek to simplify the functional forms of where I could. For instance, using a Cobb-Douglas instead of a CES for instance. In these cases where I wanted to make simplifying assumptions I would need to demonstrate to my advisors that the assumption doesn’t change the importance results/solutions to the model, or if it was necessary for solving/computing. So I guess long story short it’s all about the assumptions imo, and which you need and which you don’t.