This is one of those really handy features from SolidWorks that is noticeable by its absense when you switch over.
Basically, a lot of the time when you're designing something you don't have a precise idea of what the dimensions should be. E.g. you know that it'll be somewhere around 500mm, but you want to play around with the dimension until it looks right. An easy way to do this is by hovering the mouse over the dimension edit box, then using the mouse wheel to increment and decrement the value. This very quickly lets you modify the dimension until it looks right. Currently in Inventor we have to keep entereing values one by one, which takes some time.
I've seem a similar (archived) idea where many people worried that users would get confused because they use the mouse wheel for zoom. But really, the dimension box is a very small area and you only hover your mouse over it when you are interested in changing the dimensions. It's really quite intuitive.
