In a .vimrc, is `set nocompatible` completely useless?

Question

Several users in this epic question put the following in the .vimrc:

\" Necesary for lots of cool vim things
set nocompatible

Answer 1

Many people share their .vimrc files on GitHub and I sometimes will test out settings without replacing my .vimrc file. vim allows me to do this with the -u flag.

vim -u test_vimrc

From vim ":help nocompatible"

(Note: This doesn't happen for the system-wide vimrc or gvimrc file, nor for a file given with the |-u| argument).

This means that if you share your .vimrc with someone and they use -u flag to load your file, vim won't be configured the same as if the file were named .vimrc and located in your home directory.