Tax holiday for L.A. businesses?

City officials, including the mayor and a couple of city councilmen, proposed a three-year tax exemption for businesses that open in the city of Los Angeles. The idea is that any tax revenue loss would be offset by the companies and their workers purchasing goods and services from other local businesses. A USC business professor said that the plan would lead to the creation of 55,000 jobs. I haven't seen any specifics about time frame, which is sort of a big deal in assessing whether the tax holiday makes sense. Are we talking three years? Ten? Fifty? You can extrapolate job creation any which way you want - just plug the right numbers into the model. These things typically don't have a great track record. Heck, if it were that easy to create 55,000 jobs, wouldn't the idea already have come up, not just in L.A. but all over the country?