Smooth Like Skippy
Before they really understood how to direct light into a stone and reflect it back out again to the eye via faceting techniques, they were looking to polish a gem so one could admire its color in its largest possible form. The cabochon served that purpose very well.
Cabochon polishing predates the advent of gemstone and diamond faceting. It was relatively easier to accomplish, requiring just rudimentary tools of the time. Around the 14th century AD, however faceting began to evolve; likely originating in The Netherlands, France or Belgium. Today, the art of faceting gemstones has risen exponentially. But there are still reasons one would apply the cabochon technique.
In general, opaque stones are well suited for cabbing because the cutter is not trying accomplish any light reflection.
Finally, several stones naturally lend themselves to cabbing because of their own composition. Stones with adularescence like moonstone are a superb example. These stones flaunt their phenomenon when carved into cabochons.
Opals with their play of color can only be fully experienced when cut en cabochon.
A similar characteristic called labradoresence is a rainbow-like reflective trait seen in labradorite.
Myriad stones with long silky inclusions must be cut en cabochon to reveal their cat's eye or star effect.
This beautiful gemstone treatment may be centuries old, but it's as modern and as smooth like Skippy.