In linked hierarchies the transformations applied to an object are transferred to it's children. What happens, if both objects - parent and child - are selected and you apply a transformation (i.e. a move by 1 unit)?
The parent is moved by 1... no suprise... and it moves the children by 1. The children itself is also moved by 1, so it effectively is moved by 2 units!

Now look to the situation at the right:

Here we have a linked chain of cylinders, each cylinder is parent of the next smaller one. If we select all the cylinders and move them, then the biggest cylinder moves by 1 unit, the second by 2, the third by 3.... and so on!

This can be used for a lot of nice effects ;-)