when you are working with sheet metal you want the ability to modify the geometry of a flat pattern for an example holes, bevels ect.
now all the geometry changes that you will make on the flat pattern will be removed after going back to folded part.
the need for that came from our need to drill a beam in folded state and make a spiral out of it, the drill are for stairs assembly.
another example, if you want to make a cone with bevels at the sides you cannot do it in the flat pattern.