Some excellent answers already, not much to add... except that one or two people are making the (all to common) mistake of thinking that what works in one aircraft/scenario will work in all aircraft/scenarios.
In many types, it is true that you would normally use a cruise climb, with a speed well above Vy, when climbing en route. But there are also plenty of types with low-powered engines, where engine cooling is not a problem but climb performance may be, where making every climb Vy (unless Vx is called for) might be appropriate.
I can also think of examples where Vx would be appropriate for an en-route climb. Two that immediately spring to mind would be climbing through a gap in clouds, where Vx might be required to maintain VMC through the climb; and a climb to comply with an ATC requirement such as "cleared to enter controlled airspace level at 7000 feet", where you are perhaps too close to the boundary of the airspace to be able to be at 7000 feet in time unless you climb at Vx.
One size does not fit all!
FFF
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