Here's an example of what it can't do. I was recently messing around with the Plaid API, building sqlalchemy models for the Plaid API objects and defining relationships between them. After about 45 minutes of playing around, I got about 80% of the way to what I created without ChatGPT. It saved me a bunch of time googling around for documentation, but it gave me an absolute garbage password encryption implementation that was literally copied out of an intro tutorial I had read elsewhere, didn't even seem to recognize that there is a Password field type in sqlalchemy_utils, and omitted a bunch of key aspects of the model relationships. It also used field arguments that were either deprecated or not best practice for what I wanted to do. I also had to ask it to model every object individually, even though I specifically asked it to model all of the fields necessary to implement transactions.
Now I could go and ask it to specifically modify those things, but it doesn't "know" the best way of building this set of models. It gives me the statistically determined output of what it has consumed from all of the answered questions on stackexchange and tutorials it has been fed, and provides a halfway decent starting point, but to get from there to a working application requires actually understanding why you might build a model one way rather than another. You need to understand exactly what behavior you want to see when you delete a user, and what needs to happen to all of the related objects. You need to know that id columns should be UUIDs and not integers or strings, which is something you commonly see in tutorials but you would (hopefully) never see in a production application. All of this knowledge is the result of years of experience building applications and knowing not only what to do, but why you do it and in what context. ChatGPT is very useful reference library. It blows google searching for examples out of the water, but you need to be very careful with the results, and very knowledgeable to use them properly.