Title is self explanatory. I have a very simple understanding of QE - fed whips out cash out of thin air, buys bonds and keeps interest rates low. Why is this a good thing? Isnt this just devaluing the dollar by increasing supply?

Here's how the fed works.Title is self explanatory. I have a very simple understanding of QE - fed whips out cash out of thin air, buys bonds and keeps interest rates low. Why is this a good thing? Isnt this just devaluing the dollar by increasing supply?
that's cool, I get a car, the salesman gets a steak, and the waitress gets a toy.The fed buys bonds in the open market (a lot of them). This keeps rates low because banks know they are lend you money to buy a house, package it in a bond and sell it to the fed. They can lend at a lower rate as their risks are less.
The fed isn't printing money and dumping it into the system (like a huge counterfeiting operation). The money will eventually come out of the system when the bonds come due and the homeowner in the above example pays his mortgage off to the bank and then the bank pays the fed off for the bond that it sold.
By keeping rates low and allowing the banks to feel comfortable that they won't have a lot of bad debt on the books if the economy goes south, the banks can lend out more money. The more they lend, the better the economy will perform. Additionally the lower the interest rates, the easier it is to justify making investments (going to the bank in the first place to borrow money). This is also positive on the economy as it increases spending.
As economic activity increases, it begets more economic activity. (I buy a new car (with money borrowed from the bank), the car salesman takes his check and orders a nice steak dinner, and the waitress goes and buys a toy for her kid with the tip she got).
This probably saved the economy in 2008-2009. Today, it's probably not necessary.
that's cool, I get a car, the salesman gets a steak, and the waitress gets a toy.
and the fed gets their money back when I pay off my auto loan.
What happens with all the sub prime auto buyers that don't pay?