The thing is once you can code in emacs, and even when you can use the keyboard macro utility, you constantly find little time saving ways to use it. At first though they're not even time saving, they take longer. Anyhow some examples:

I have a function for my work log which gets the date, figures out the previous Monday's date and dumps a formatted weekly log for me to fill out.

I wrote an entire budget tracking application which generates a forecast and dumps it to a csv file

Wrote a utility to mark and optionally delete duplicate files in a dired buffer

Convert a windows path name to a cygwin one

Functions to add local sales tax and remove local sales tax, same for tips.

Perforce source control, helpers to do blame functionality and other stuff that benefits from pulling Perforce output into a buffer

The most used feature would be keyboard macros which are endlessly useful for any repetitive editing task, which can show up unexpectedly at any point of the day

Occasionally have to write throw away custom code to create some boiler plate code, such as turn the API documentation for some errors into a C++ array of structures that can be manipulated in code

Full client for Redis