Quite a lot of things. A (probably non-exhaustive, off the top of my head) of things where it saves me the most time:
- Bureaucracy. Writing silly boilerplate, e.g. data management plans or gender perspective statements in grant proposals.
- Cutting or expanding text (we routinely have lots of forms and submissions where you need to write a text in a given word or character range).
- Polite emails in English to people I don't know much (e.g. "Write a polite professional email reminding this person that the deadline for reviewing paper Y expired yesterday...")
- Brainstorming. "Give me 10 ideas about research direction in topic X". It won't give great ideas, but it's good to set the mind rolling.
- Routine scripts/code used in experiments and papers: write a Python script to make a box plot with such and such data, or to take a file in this format and strip this unneeded content, etc. The typical kind of code that appears a lot in research, is trivial to code but consumes time and ChatGPT does it in seconds.
- Suggest titles (paper titles, grant proposal titles, etc.).
- Suggest ideas for exercises or exam questions (e.g. write an assignment that can be solved with the coin change algorithm but involves no coins or currency).
- How to do X in Excel (although the problem here is that my Excel is in Spanish - why, why did they decide to translate function names? - and it's not that good at that - but anyway, it's very useful).
The productivity boost is very noticeable, well worth the cost, even if it hurts to pay out of pocket for a tool used at work.
