This will encourage trading. We will still have a 35-man roster limit after the FA draft.
It is one less thing for the commish to keep track of, which lets him keep track of the necessary things more easily.
With the farm setup, a 35-man roster limit year-round results in teams that are playing for the future having to release players they may wish to keep, but who will have no value for a year or two.
With no limit, they won't have to make that decision but once a year.