Understanding why mode keyword shouldn't be used for minor modes in .dir-locals.el

[Kaushal Modi]

Hello,

>From the manual node (emacs) Specifying File Variables:

> Do not use the ‘mode’ keyword for minor modes.  To enable or disable
a minor mode in a local variables list, use the ‘eval’ keyword with a
Lisp expression that runs the mode command (*note Minor Modes::).

Though, I have been using (mode . auto-fill) in my .dir-locals.el for ages,
and it works great. And it's less verbose than (eval . (auto-fill-mode)).

So I'd like to understand why the manual suggests *not* to use the mode
keyword for minor modes.

Thanks.

--
Kaushal Modi