A lot of processes don't handle ENOMEM well. Your mail client asks for memory for a buffer to write an email and it gets ENOMEM, what's it going to do? Silently fail to do anything? Pop up an error message (which will probably take memory to display)? Exit?
Pop up an error message (which will probably take memory to display)?
I don't know how common this is on the Linux/POSIX side, but in DOS and Windows it is usual practice to allocate some amount of memory at startup and use that for error-handling code, so that things like showing error messages will not cause any more allocations.
