I understand that 'out of memory!' would flash when the buffer is not autoflushed in such cases....

I'm not aware of any such cases. That doesn't mean that they don't exist, merely that I've never heard of any.

Buffers tend to be something like 4k on modern Linux-style systems. I have trouble imagining a system on which saving 4k is the difference between completing a task and running out of memory, at least with Perl. (If I had to write such a program, I'd use C and forbid dynamic allocation.)