I once got called in to help track down a periodic crash in an EDIF reader. Almost immediately I started getting a headache. The original author seemed to feel that Yacc was going to penalize him for whitespace, and his Yacc grammar was a dense, unreadable mess. I spent a couple of hours formatting it, adding rules for missing terminals as they emerged, structuring the declarations to avoid stack growth, and voila, the crash was extinguished.
So remember, for every time you wait while Yacc processes your grammar, there will be thousands of runs with the generated parser. Don't be cheap with the whitespace!
