Because it is said that centimeters are lost?

For example if you lengthen 5 they say they really are 4 ...

Looking at the femur in image, no matter how much curvature this bone has, if you cut it apart and join the gap, it is still 5 and not 4.

Will it really be a problem with some devices that do not support the weight and when they do create a bit of compression in the mechanism?