There have been various times in my programming career that I've wanted an emacs macro with arguments, so that it would do things like concatenate a number in each line. Things like this in C: #define a 0 #define b 1 ... #define l 10 #define m 11 Usually I take that as a sign that I need to write some other program to generate the lines of the C program, but for some tasks that's overkill and I want an automated way…
I'll fill one buffer with the text I'm editing, and the other buffer with any 'arguments'. Then I'll just write the macro to switch between buffers and grab arguments as necessary.