The systems can be of 2 types. Push systems or Pull systems.

Push systems mean we the owners, keep pushing work into the pipeline as much as possible with the hope that it would get processed and it would lead to maximum utilization. Whereas in Pull system, we design the system in such a way that it pulls the material from outside as and when the bandwidth frees up. So, velocity or efficiency is consistent.

Pull-based systems are a kind of JIT [Just in time environments].

Queuing theory and flow concepts align with it in the manner, that in ORDER to have efficient operations with good velocity and if you are trusting the system to pull the material as needed then the ENTIRE flow in the pipeline needs to be smooth and uniform. And flow can be uniform if it ADHERES to querying theory that essentially says that only enough work should be QUEUED for each node that can be processed without creating bottlenecks.

So, this way, these three concepts build WIP [Work in progress] limit concepts of Kanban.