Pull processes do not only play an important role in lean approaches such as Kanban, they are also fundamental to Scrum: Applying the framework generates a pull process where teams pull work from the product backlog into the sprint. Understanding what a pull process is and how it works helps you apply Scrum and Kanban effectively.
The easiest way for me to illustrate the difference between push and pull is to evoke a childhood experience you may share with me: drying the dishes. I vividly remember being called into the kitchen after Sunday dinner where my mum had already piled up the clean wet dishes. Even though I would frantically try to reduce the size of the pile in front of me, I always ended up finishing off the job long after my mum had retreated to the living room together with the rest of the family.
Now imagine running cleaning and drying the dishes in pull mode. The first thing my mum and I would do is to agree on a small buffer of clean wet dishes, say three. I would then wait for my mum to populate the buffer. As long as the buffer is full, my mum is not able to clean any new dishes. Only once I have started drying one of the dishes, she would clean the next dish.
Establishing a pull process changes how work is carried out: It closely links formerly disjointed process steps; problems and impediments now surface quickly. A pull process eliminates waste such as partially done work (also called work-in-progress or WIP). What's more, it creates a sustainable pace by avoiding overburden: In Scrum, the team determines how much work they can pull into the sprint and hence manages its own workload. In Kanban, WIP limits ensure that demand is matched to capacity.
Be aware that establishing pull usually involves disruptive change. It it requires that the people carrying out the work take on ownership and are empowered. Work can no longer be pushed onto anyone. It now has to be pulled along.