I am currently writing an article on tithing so the comments on this thread have proved very interesting.
My understanding of the tithing from research is:
God gave Israel tithing laws for definite purposes, apparently involving the use of two tenths of their annual income, except during the Sabbath years, when no tithe was paid, since no income was anticipated. (Lev 25:1-12) However, some scholars believe there was only one tithe. Such tithes were in addition to the firstfruits they were under obligation to offer to God.—Ex 23:19; 34:26.
The first consisted of one tenth of the produce of the land and fruit trees and of the herds and flocks. This was brought to the sanctuary and given to the Levites because they had no inheritance in the land but were devoted to the service of the sanctuary. They, in turn, gave a tenth of what they received to the Aaronic priesthood for their support.
The second tenth, was set aside each year for purposes other than the support of the Levitical priesthood, though the Levites shared in it. Normally it was used by the Israelite family when assembling together at the national festivals. In cases where the distance to Jerusalem was too great for the convenient transport of this tithe, then the produce was converted into money and this, in turn, was used in Jerusalem for the household’s sustenance and enjoyment during the holy convention there.
But at the end of every third and sixth years of the seven-year sabbatical cycle, this tithe, instead of being used for expenses at the assemblies, was set aside for the Levites, alien residents, widows, and fatherless boys in the local community.
So it would appear that the tithes were also a "social benefit" system.