The roughing cutter has a special 'serrated' cutting edge which breaks up the chips coming of the machine. This reduces heat on the cutter and the material and improves dust extraction.
Up cut refers to the direction of the flute. As the router bit grooves, slots and cuts the chips are forced upwards. Therefore, the best finish is on the underside of the cut part. Up cut spirals are not recommended for softer materials such as MDF as the finish on the top surface is often ragged. Up-cut spirals can run at higher speeds but require good quality suction on the table to prevent material tug.
Three flute router bits have a smooth cutting action and a greater finish in harder materials. Three flute router bits last longer, run faster feed rates and are less susceptible to breaks than one and two flute router bits.