It's supposed to be a part of basic income to pay enough for someone to be able to afford rent and to and choose where to live that's within their budget. If it was a separate thing, perhaps people could be given a choice among places with a low cost of living, and then the amount needed for basic income would be lower. http://marshallbrain.com/manna1.htm
Edit: Manna was more relevant than I thought:
> The government had finally figured out that giving choices to people on welfare was not such a great idea, and it was also expensive. Instead of giving people a welfare check, they started putting welfare recipients directly into government housing and serving them meals in a cafeteria. If the government could drive the cost of that housing and food down, it minimized the amount of money they had to spend per welfare recipient.