Why is it suggested to freeze Chimichurri Sauce?
There is a risk of botulism growth.  C. botulinum grows in the absence of oxygen (an anaerobic environment).  It is possible that botulinum spores are present on the garlic, as well as the herbs. The spores exist fairly widely in our environment, but they don't grow and develop toxins unless the conditions are right. The recipe results in a sauce that places these ingredients in an anaerobic environment, significantly raising the risk of botulinum growth.  Colder temperatures reduce the risk.  That is why freezing and refrigeration (and the associated time limits) are recommended.