those receiving aid from the government are consumers. Consumers spend money in stores, which pays the bills of the people who own those stores.
by giving money to people who would otherwise not have much - you add consumerism and therefore social Awelfare MORE THAN PAYS FOR ITSELF as well.
Before the government can give money to one person, via welfare, or any other form... They must first take more money away from another person. Then the bureaucracies loose more the half the money (seemingly into thin air.) Then 80% of the remaining money, (that should be used to buy food for people who are actually needy,) is misappropriated by persons who should have never received aid to begin with... I don't see how that stimulates the economy, seems to me, it would work much better, to just not take the money from guy A, and let him spend/save it how he sees fit.