Task: Question Answering
Input (English): $\mathit {\texttt {+}PPMI}$ only falters on the RW and analogy tasks, and we hypothesize this is where $\mathit {\texttt {-}PMI}$ is useful: in the absence of positive information, negative information can be used to improve rare word representations and word analogies. 
 Question: What are the disadvantages to clipping negative PMI?
Output (English): It may lead to poor rare word representations and word analogies.