Lead Time is the amount of time it takes from the start of a process to its completion. You can define the process to include – or exclude – activities done prior to the order such as costing a proposal, or after completion such as billing.
We exploit Little's Law, which states that process lead time is equal to the number of "things" in process (WIP inventory) divided by the number of completions per hour (throughput), to shorten lead time. Simply stated, at a constant throughput rate, a decrease in WIP causes a corresponding decrease in lead time.
Batch operations create inventory throughout the process: before the start of the process where in manufacturing it may be called "safety stock," or in repair businesses it may be called "backlog;" ahead of an operation where it would be called "buffer stock;" after an operation where it may be called "accumulation;" or at the end of the process where it would be called "finished goods."
Inventory traditionally is used to protect the process against contingencies. Eliminate the underlying cause for maintaining that inventory and enjoy the benefits of much shorter lead times.