Foils, laminates and many other materials are not homogeneous in thickness. Besides inner tension is released during processing, which results in different lengths during rewinding. Each roll has its own web tension and diameter during the winding process which can lead to cores that are too tight. In the worst case, the web can be torn apart. Or, the web can form a slack due to the different lengths and the winding quality would not be optimal. In some cases, this would even make a new rewinding impossible. Wastage and higher costs are the consequences!