Why not position columns absolutely?

Positioning a column with absolute really has no benefit and causes more issues than it's worth in different situations. You should only ever absolutely position an element if it's needed, for example if you want to position an element within another div without having to change the markup of your HTML. Using position absolute can have many benefits, but learning how and when to use it is a learning curve.

When making changes to your code at a later date, you may find many unwated problems as a result, especially since you're taking the absolutely positioned div out of the flow of the document.

An example of when i may use position: absolute; is when i want to position a ribbon that says, let's say for the sake of the example "Featured" and i want it to appear in the top right side of a div, but has to sit slightly outside of the div in order to have the effect of it wrapping around the div - i.e. look at this example; http://jsfiddle.net/chriscoyier/H6rQ6/1/

Generally you would create an image for a ribbon like this since it is a much more cross-browser compatible method.