This table lists the various kinds of federal spending and their effects on GDP. The higher the effect, the more valuable as a 'stimulus' to the economy. It clearly shows that tax cuts for the well-to-do have the least effect as an anti-recession measure.
Why then are Republicans and Democrat centrists pushing them? Because they basically represent the wealthy, that's why. It isn't a matter of trying to address the recession, it's a matter of the letting the rich keep their money. Which I suppose I can understand, if you're a wealthy person, or if you receive political contributions from them.