[fintstone]

Seems like they are used to establish the length of time one has been here working illegally...as that is a prime consideration for amnesty.

As far as I know, filing under an ITIN does not prevent an illegal from accessing social welfare.

If an immigrant later becomes eligible for Social Security, earnings reported with an ITIN may be counted toward the amount he or she is eligible to receive.

It also allows them to work for an employer who needs a way to file taxes on wages....and allows the immigrant to get a tax return.