vim - 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

But is it really necessary? From the docs:

'compatible' 'cp'
    boolean (default on, off when a |vimrc| or |gvimrc| file is found)

If set nocompatible is going in a .vimrc, that means that a .vimrc file exists, seemingly making it pointless.

Answer 1

If it is the system-wide vimrc, this option won't be off. So, if you're changing the system-wide vimrc and you want it, you need to set it.

From the documentation section *compatible-default* (emphasis mine):

When Vim starts, the 'compatible' option is on. This will be used when Vim starts its initializations. But as soon as a user vimrc file is found, or a vimrc file in the current directory, or the "VIMINIT" environment variable is set, it will be set to 'nocompatible'.

Another difference is that explicitly setting 'nocompatible' overrules calling vim with the -C flag.

In any other scenario, yes, setting 'nocompatible' in your vimrc is a noop.

In the end I think it's just a matter of "better safe than sorry".