By far the biggest timesaver has been having it write shell scripts for any task that's even a little tedious. I'm not good at shell scripts, so this would typically never be worthwhile for me to do for any one-off task.
Generally anything where I'm working with technology I'm not an expert on, and might not find it worth it to do learn the thing just to get the task at hand done.
Prompt: "write a powershell script that uses imagemagick to find all .pngs in a given directory, resize them to 400x400, don't squish them and put them in the bottom right if the aspect ratios don't match. apply a mask found in mask.png, convert to jpeg, and rename them removing all spaces from the name, and remove all leading digits and underscores from the name"
This worked right out of the bat. I also didn't know how to make the image mask so I had it teach me that too.
If I was doing this on my own, I'd have had to look up all the imagemagick parameters, I'd have done it as a batch file, and had to look up all the batch file scaffolding required. The powershell script ended up nicer than the batch file would have been, but then I realized I wanted to run it on macos too, so I had it translate it to a zsh script for macos.
Prompt: "i have two directories with a bunch of images in them, i want to merge both directories to a third directory, and any time there's a file with the same name in both directories, i want to view both files and pick which one to keep."
Again, I had it do it both in powershell and as a zsh script. I'd likely have just done this task by hand without even considering scripting it, it was like 100 images I needed to sort through. I'm also actually gonna have to do it again, which I hadn't realized at the time.
Prompt: "i need a formula for google sheets that tells me if the words in two cells have any letters in common".
Once again this is something that I'm not familiar with, I'v never done much with spreadsheets, and would have to look up a whole lot to produce something that works, and it just made it for me. I run a wordle variant called xordle that takes puzzle submissions from users, they often give me invalid puzzles, this change to the submission form will make it so I can tell immediately if a puzzle is invalid.