Abrasives help to remove dead skin cells, dirt, sebum and all other stuff that covers your skin. Unlike Exfoliants which act chemically, abrasives remove dirt physically. They literally scrape everything out of the surface.
Many professional skincare specialists advice to avoid abrasives because they are too aggressive. They can do more bad things than good. They can damage your skin or irritate it. That’s why you should apply products with abrasives gently, without heavy pressure. Your skin will thank you for this.