Side cutters or angle cutters, cut on an angle, meaning the wire edge will be cut to one side.
The choice of use is totally up to you, the wire jewelry maker. For example, if you are cutting jump rings, a flush cutter will allow the jump ring to be closed on a level plane, whereas when using an angle cutter to make jump rings, you would need to cut both ends of the jump ring at opposite angles to make it fit together smoothly. This is also known as "double cutting."
Answer contributed by Dale "Cougar" Armstrong