The beater bars in a rotary vacuum (that rolling cylinder brush at the bottom) pry into the carpet fibers by pulling on the rug, thereby loosening dirt more efficiently. While this may sound great, the result is actually increased shedding, possible damage to the wool fibers, and reduced rug lifespan. It’s especially important to avoid vacuuming the fringes using a vacuum with a beater bar, as the bar will pull the fringes and may cause unevenness in the weave overtime—it’s similar to what happens when a thread on your wool sweater gets caught on your nail!