Hi Amber
the binding is a two ways binding. That's whenever the value in the input control changes that model will change too. this is one of the most powerful feature in SAPUI5. A very comprehensive model and control binding mechanism
To help you understand this better, we have another sample
JS Bin - Collaborative JavaScript Debugging
Change the value in the first input and click on the Check Model button. you can see that the model value is changed accordingly.
But change the value in the second input and click on the Check Model button. you can see that the model value remains unchanged.
Thanks
-D