I wrote about using it to explain code (and mathematical formulas and suchlike) a few weeks ago: https://simonwillison.net/2022/Jul/9/gpt-3-explain-code/
I've been experimenting with using it to build a human-language-to-SQL tool, so that people can ask questions of their data "what country had the highest GDP in 2019" and it will turn them into the correct SQL query, given a table schema. I'm still iterating on this but it's shown some very promising initial results.
I use it a lot when I need to get something small working in a language that I don't have day-to-day familiarity with. "Write a bash script that loops through every MOV file in this folder and extracts the audio as MP3" is a good example of that kind of prompt.
Riley Goodside on Twitter posts weird and interesting new things you can do with GPT-3 on a daily basis: https://twitter.com/goodside/ - his instructional template trick was on HN the other day, it's really clever: https://news.ycombinator.com/item?id=32532875