When you cut taxes and/or increase financial aid (certainly unemployment, anyway) to the poor and the middle classes, it stimulates the economy because they're in a position where they can't not spend it.
The rich already got money and are probably already spending everything they're comfortable spending at the moment, so it goes generally into their various reserves... or into investments that just redistribute capital amoungst the wealthy without stimulating the broader economy... or at best, go into luxury purchases that have little effect on the larger economy as they're produced by themselves-wealthy artisans or wholly overseas or are large collectables purchases that, again, simply redistribute wealth amongst the rich.
If I were obscenely wealthy and I, say, purchased a Honus Wagner card for a million and a half dollars, it would be awesome for me to have that card and all that but the money I spent would go largely to the dude who previously owned the card and to a lesser extent to some already upperclass suits at the auction house.
1.5 million in unemployment checks to 10,000 laid-off folks will probably end up buying... food from local grocery stores, gasoline from the local gas station, maybe a few extra Christmas gifts from the mall up the road... directly getting the overall American economy churning again.
Whatever else we're talking about here, remember: there is no logical defense of trickle-down economics. IDEO-logically, sure, but not logically.