The purpose of a retroactive legalization is the possibility of upping the assumed value and credibility of possible bargaining chips. Like automobile dealers do when they add on prices for 'dealer prep' not only out of all proportion to the preparation they do on a car prior to delivery, but also contrary to their contract with the manufacturer. It's added on so that it can be subtracted, at no cost to the dealer!
Northern California wildfire doubles in size, displaces thousands (Reuters)
from the article: Israel hints it may retroactively legalize settlement construction