Cam has some machinery element having some optional form. It gives an optional motion to the other side by the direct contact.
It's enough for only one side. having an optional motion for giving an optional working. So the other side is generally used with a simple shape of roller or plane.

Cubic cam (three dimensional cam) generally can make smaller capacity of occupying in space as compared with plane cam.
And it is used to many automatic machine by making any glyph cam or "rib cam" with working closed cam of reliability motion.