Support 3D printing filaments are used primarily in dual-nozzle printing. Their key feature is that they can be easily and safely removed by dissolving in a solvent that does not effect the main print. This infers the ability to print significantly more complex designs with supports that can be removed without structurally or visually damaging the final product.
Support plastics will be more suited for use with specific plastic types, depending on their solvents. For example, HIPS is commonly used as a support material for ABS as HIPS can be dissolved in Limonene, which does not effect ABS. Similarly, PVA is used as support for PLA as it can be easily dissolved in water and they print at similar temperatures.
The printing temperature of the support material should be as close to the printing temperature of the primary filament as possible, this prevents any warping that may occur if one of the plastics heats the other above its melting temperature.