The word masticating means "chewing". A masticating juicer extract juice by chewing and grinding the produce. Masticating juicers are sometimes also called slow juicer. This is because they rotate at slow speed. Speed of a masticating juicer vary from 80 to 100 rpm.
Next obvious question is why to purchase a juicer that rotates slow?
High speed juices produce heat during juicing process and kill several vital nutrients and enzymes. That is why many people prefer slow juicers.They keep all the nutrients intact in juices.
Masticating juicers also give high yeild relative to centrifugal juicers aka fast juicers. They dont waste organic produce and leave very dry pulp.
Another advantage offered by masticating juicers is ability to juice everything ranging from fruits, vegetables to leafy greens. A centrifugal juicer can't juice greens effectively.
Disadvantage of masticating juicers is that they are slow and they are litle tough to clean relative to centrifugal juicers.
Check out the best masticating juicers here http://www.bestjuicer.biz/best-masticating-juicer-reviews/