Limiting Work In Progress in Kanban --- Effect or Side Effect

I was going through the kanban guide and it says under topic of "Limiting Work in Progress (WIP)" that The primary effect of limiting WIP is that it creates a pull system. It is called a pull system because the team starts work (i.e. pulls) on an item only when clear that it has the capacity to do so. When the WIP drops below the defined limit, that is the signal to start new work. Note this is different from a push system, which demands that work starts on an item whenever it is requested.