Is there any situation where you wouldn't want include guards?

Question

I know why include guards exist, and that #pragma once is not standard and thus not supported by all compilers etc.

My question is of a different kind:<

Answer 1

Suppose you have a third party library, and you can't modify its code. Now suppose including files from this library generates compiler warnings. You would normally want to compile your own code at high warning levels, but doing so would generate a large set of warnings from using the library. You could write warning disabler/enabler headers that you could then wrap around the third party library, and they should be able to be included multiple times.

Another more sophisticated kind of use is Boost's Preprocessor iteration construct: http://www.boost.org/doc/libs/1_46_0/libs/preprocessor/doc/index.html