They actually combine three processes: Slubbing, intermediate, and roving, and their aim is to draw the sliver out until it is thinner, more uniform, and cleaner for spinning.
"Carl and the Cotton Gin"
Sara Ware Bassett
It will be understood that these recipes are applicable to all kinds of woollen fabrics, loose wool, Slubbing, yarns in any form, woven worsted or woollen cloths, felts of any kind, etc.
"The Dyeing of Woollen Fabrics"
Franklin Beech