is running autoheader mandatory?

[Andrew Makhorin]

Hi,

I am a maintainer of a GNU project. Until recently I used autoheader
to produce config.h.in. However, for various reasons I decided not to
use autoheader at all, preparing config.h.in manually. Is it correct?
If so, is it correct to write
   AC_DEFINE([FOO],[1])
rather than
   AC_DEFINE([FOO],[1],[some text])
in configure.ac? This works ok without autoheader.

If running autoheader is mandatory, could anyone please explain me why?

Thank you,

Andrew Makhorin