Show the tip first:
vim --cleanto start a “clean” vim, and then use the macro.
It is a very very simple tip, but helped me a lot yesterday. I recorded a macro to exchange two word-lines in a long text file. Repeating the macro more than 50000 lines is really slow. A few minutes later, I got some messages from vim then found the culprit. There were too many autocmds and plugins slowing current buffer. After restarting Vim with
vim --clean, the whole progress was lightning fast.