What is the difference between single rotary cutting knife and double rotary cutting knife ?

Single rotary cutting is like a knife, double rotary knife is like scissors,So paper cutting side should be more smooth by double rotary cutting knife,especially for paper above 300gsm.So single rotary is suitable for thin paper, double rotary is suitable for thick paper, and after cutting from double rotary, paper can be used for offset printing machine directly. And single blade cannot because of more dust at the cutting side.