First of all, what is “Lead Time”?
Simply stated, “Lead Time” is the amount of time that passes from the start of a process until its conclusion.

McDonalds Cartoon — drive through placement (push), to order processing (pull), to order fulfilled (done).
The shorter the Lead Time is, the better… meaning, we get feedback to what has concluded; and with fast feedback, we get to learn fast as well and use / invest that feedback — and the “learnings” that came with it — into something useful.
Applications in real life: