In many cases trading in non-deterministic choice for deterministic choice (ie, parsing expression grammars) makes reasoning about and writing grammars much easier. For example, in the case of the arithmetic expressions grammar the rules should work as-is to get precedence.<p>Oddly you would think that sacrificing non-determinism would really hurt the power of PEGs to express languages but there are languages that are not context free (eg, `a^nb^nc^n`) that can be written as a PEG.