"The resources looted by the player destroying the Construction Yards will now be based on how much the player striking the killing blow has also contributed to the destruction of the defense units. The difference in resources between that amount of loot, that the last player receives and the total value of the base is lost."
I guess if a friends hits a base one time and dealt 50% to the defense units, then the player who kills the CY in the next shot will only get 50% of the total recourses that are left, while the other 50% gets lost. Thats how I understand it.
This will indeed be a nerf to groupplay (but also will make multiaccounting less efficient).