http://www.immigrationpolicy.org/just-facts/facts-about-individual-tax-identification-number-itinITIN holders pay taxes.
ITINs let more people pay into the system, which builds the tax base. Between 1996 and 2003, more than 7.2 million ITINs were issued. More than $300 million was collected in taxes in 2001 alone from ITIN filers—a large portion of whom are undocumented.
ITIN holders are not eligible for all of the tax benefits and public benefits that U.S. citizens and other taxpayers can receive. For example, an ITIN holder is not eligible for Social Security benefits or the Earned Income Tax Credit (EITC). However, if that person becomes eligible for Social Security in the future (through legalizing his or her status, for example), the earnings reported with an ITIN may be counted toward the amount he or she is eligible to receive.
ITINs do NOT provide immigration benefits.
An ITIN does not provide legal immigration status. It is not a document that can be used to prove legal presence in the U.S.
An ITIN does not provide work authorization and it cannot be used to prove work authorization on an I-9 form.