Throughput is the volume of work completed in a period. Lead time is how long a customer waits from request to completion. Cycle time is how long the work itself takes once started.
The gap between lead time and cycle time is waiting, and in most service businesses the waiting is the larger part.
The constraint governs
Output is set by the tightest point in the chain, not by average effort. Adding capacity anywhere else changes nothing.
In a trade business the constraint is usually one of: available technicians, the hours in a day after travel, or a single person who must approve or diagnose.
Working out which one is binding is the whole exercise. Effort spent elsewhere feels productive and moves nothing.
Work in progress
Jobs started and not finished. A large amount of it is a warning rather than a sign of activity: it ties up materials and cash, and each unfinished job carries a cost to return to it.
Finishing work already started is almost always more valuable than starting more.
What lengthens lead time in a trade
Travel between jobs — see tickets per route.
Parts not on the van, which turns one visit into two.
Return visits to correct work — see reducing callbacks. Every one consumes capacity that could have served a new customer.
Waiting on a decision, an approval, or access.
Why it matters commercially
Lead time is a competitive position of its own. For urgent work, the business that can come sooner wins regardless of price — see improving close rate.
And throughput is what actually limits growth — see growth capacity. Winning more work than the business can complete produces longer waits, more callbacks and worse reviews rather than more profit.