The neutron temperature example is crucial: you just can't give the cross section of a target alone, the energy of the incoming beam also matters.
Most important application: produce X-rays for X-ray crystallography.
Note however that the big experiments at CERN, like the Large Hadron Collider, are also synchrotrons.
List of facilities: en.wikipedia.org/wiki/List_of_synchrotron_radiation_facilities
Predecessor to the synchrotron.