what is the most important thing large language models can do?

The most important thing large language models can do is code generation through very good prompt pattern recognition in the LLM.  This is amazing because coding now becomes available to non-technical individuals who did not go to school to learn how to code.  If you are coding and you get stuck you could technically use a large language model to help you get unstuck in your code development.  It's still the early stages for LLM code generation but the results look extremely promising.