Right now there are 17 states that have had or are going to have a sales tax holiday this year(California not being one of them, of course).  Is there a benefit to this or is it just a promotional gimmick that politicians can talk about and economists can complain about?  See this article in the Christian Science Monitor by Richard C. Auxier, then you decide:

http://www.csmonitor.com/Business/Tax-VOX/2014/0820/Do-tax-free-holidays-make-sense

It looks like a lot of them coincide with sales tax exemptions in the states, or if a state (New York, for instance) wanted to compete with a neighbor state without a sales tax (New Jersey) and there may be other reasons for the holiday (the article touches on a couple of them).  It is interesting that few western states have these holidays (New Mexico and Texas are the farthest west.) 

Overall, I think it depends on the state and what their motivation is to have these holidays.  The states that hold them have their own agenda, and since they keep having them it is having the desired effect.

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