NegativeLiterals / Lexical negation prevent (ab)using "negative" zero.

With NegativeLiterals and LexicalNegation, -0 is desugared as fromInteger (-0 :: Integer) = fromInteger (0 :: Integer).

That prevents some tricks possible in Haskell98.

One concrete example is e.g. SAT literals, with variables usually being natural numbers: 0, 1, 2, 3, ... And positive literals being 0, 1, 2, 3 and negative literals -0 -1 -2 -3 -4. DIMACS format explicitly starts variables from 1 instead of 0 so negate can be used to negate literals. But e.g. minisat implementation uses one bit of the unsigned word to indicate literal positivity (negLit lit = complementBit lit 0, litToVar lit = shiftR lit 1; this encoding has another benefits).

My point is that: Negativeliterals and LexicalNegation can change the meaning of program.

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I think the information should be at least reflected in the docs. People who (ab)use Num for (mostly) overloaded numeral literals should be warned (Num doesn't have a law that negate . fromIntegral = fromIntegral . negate!). Also IMO this subtlety is on the way of including either extension in GHC20xx language versions. fromInteger in Num is not a great design.