Quantitative easing helps the economy in three other ways.
QE Keeps Bond Yields Low
The federal government auctions off large quantities of Treasuries to pay for expansionary fiscal policy. It increases demand as the Fed buys Treasuries, keeping Treasury yields low. (There's an inverse relationship between yields and prices with bonds.)
QE through buying treasuries therefore also keeps auto, furniture, and other consumer debt rates affordable. The same is true for long-term, fixed-interest debt. It supports the housing market when mortgage rates are kept low, and low rates on corporate bonds make it affordable for businesses to expand.
Increasing the money supply also keeps the value of the USD low. U.S. stocks are more attractive to foreign investors when the dollar is weaker because they can get more for their money. A cheaper dollar also makes exports less expensive abroad.
In the current scenario, I believe is done to attract foreign investors and boost the buying of goods.
The only downside is that QE increases the Fed's holdings of Treasuries and other securities. For example, the Fed's balance sheet held less than $1 trillion before the 2008 financial crisis. That number had increased to almost $4.5 trillion by July 2014. But it won't create any problem for US fed res.