  We give a simple example of the tight connection between entanglement and
coherence for pure bipartite systems showing the double role played by
entanglement; it allows for the creation of superpositions of macroscopic
objects but at the same time makes subsystems lose their quantum mechanical
coherence. For this we study the time evolution of the spin coherence in the
Stern-Gerlach (SG) experiment. We also show that, contrary to the naive
intuition, the spin coherence is lost before the two beams become separated in
the spatial coordinates.
