When you add a cross-break to a sheet metal part the dimensions of the part won´t change. If the cross-break is only a few degrees (e.g. 3°) the change is insignificant.
But how do you get the size change of a part if the cross-break is 10° ?
Suppose you have two parts 1400x1400mm. One without a cross break and one with a 10° cross-break. Solidworks won´t change the flat pattern but reality si different. The part with the cross-break will be 5-6mm smaller.