I use formal verification as part of my development process. The needs of the proof guide the development of the code as much as vice-versa. The result is usually cleaner, simpler, smaller and usually more efficient programs developed much faster as debugging effort is minimal. I still create complete test cases. Proof maintenance as code changes is a pain and I would like LLMs and/or other tools to help with that. I would never try to formally verify code written with regular processes!