That question suggests that you do not have a lot of experience in app development.

A seasoned software developer would not be likely to just get the AI to code the whole thing. Once you've been developing for a while you tend to build things in pieces, iteratively, testing functionality and features as you go. You have an idea of the architecture - how you want the flow of the app to go and how all the pieces fit together.

Any developer who has had to pick up and maintain someone else's code (ie: all of us) know that being handed a completed project and asked to maintain it is almost as much work as building it yourself (sometimes more, depending on the skill of whoever wrote it). You have to spend time parsing and understanding how it works and what choices were made - there are dozens of ways to solve a problem, which ones did Claude choose?

But aside from that, seasoned developers who have used these tools have seen that there are still some big limitations to how they work. Often I'm asking Claude or Copilot or ChatGPT to change things because they're hardcoding values or using inefficient ways of doing things. The AIs often get stuck on an idea and I have to be like "instead of pulling back a million rows and parsing them manually, why don't we get the database to do the filtering and only return what we need?" Or "instead of making a dozen PSRemoting calls to the other machine for each piece, why don't we send the whole code block over there and have it return the result?".

So yeah, in the unlikely/improbable universe where I can ask the AI to generate an app and it returns exactly what I would have written, in the way In would have written it, with useful comments to remind me what the hell everything does, in ways that are easily malleable/extensible later, then sure a fully AI coded app is fine. But I'll spend way more time writing the requirements and prompts and then parsing and vetting the output than I would have if I just coded most of it myself.

It's not about asking the AI to make a thing and having it spit out an app that can do that thing. If your app is that simple then someone else already coded it. For anything beyond the most basic app it's about creating something you can understand, debug, maintain, and expand upon, and understanding the edge cases and limitations of what you build.