There are LLMs today that are amazing at coding, and when you allow it to iterate (eg. respond to compiler errors), the quality is pretty impressive. If you can run an LLM 3x faster, you can enable a much bigger feedback loop in the same period of time.
There are efforts to enable LLMs to "think" by using Chain-of-thought, where the LLM writes out reasoning in a "proof" style list of steps. Sometimes, like with a person, they'd reach a dead-end logic wise. If you can run 3x faster, you can start to run the "thought chain" as more of a "tree" where the logic is critiqued and adapted, and where many different solutions can be tried. This can all happen in parallel (well, each sub-branch).
Then there are "agent" use cases, where an LLM has to take actions on its own in response to real-world situations. Speed really impacts user-perception of quality.