It's almost useless for high-level design and architecture. Those tasks do take more time than writing code, but they're super-charged by rapid prototyping, which ChatGPT excels at. For example, right now, if I'm picking between three libraries, I can have working versions of my code implemented in all three in a few minutes, and built out a bigger mockup in a few hours. I can make a more educated decision from there. In the olden days, that'd be a few hours and many days, respectively.
It also does really nicely for code reviews, which results in better code. That also speeds up maintenance and, later, debugging. That's especially true in domains I'm less familiar with.
Some maintenance, it excels at. I'm the author of a major piece of open source infrastructure, which is widely used, well-architected, but every technology used is obsolete (JQuery, older Python web frameworks, legacy database, etc.). I feel like I could rewrite the whole thing in React+Node+etc. in a few weeks. There is close to zero architecture work -- it's mostly having GPT write -- or sometimes just translate -- code piece-by-piece.
I don't feel like GPT-4 obsoletes software engineers as it's used yet, but it does really raise the bar on what's possible to build.