It's hard to make long term plans with that, because instead of putting aside $100 at the beginning of the month, now you need to save $3 a day. With amounts that small, it's easy to accidentally overspend.
Plus sometimes sudden unexpected costs happen, and you cannot wait another week to slowly save up for it, you need that money now.
Not all poor people are poor because they're drug addicts that cannot handle money. Poverty is hard to escape. I'd rather not humiliate these people any further and make it even harder for them to lead a dignified life just because some people might waste their money in the first week.