Someone never had to bit-pack their programs to save memory, disk space, or bandwidth. In fact, it's a huge waste of memory; if you only need 3 bits, a 'char' would have sufficed. Saves 24 bits!
Of course, we could use nibbles to make data structures where the fork return value only takes up 3 bits instead of a whole byte, but that could be considered micro-optimizing. (the compiler may do this for us anyway, though)
But regardless, the point of that sentence is nothing to do with memory usage, but with semantics. Whether you or the compiler packs all the information into 3 bits or 3 words, that's fine, as long as the language helps you distinguish the parts.