What sets the pace?

A pipeline can only move as fast as its slowest stage. Every other stage has spare capacity it can never use, because work piles up behind the constraint and starves everything downstream. So speeding up a non-bottleneck does nothing for throughput — only lifting the constraintGoldratt's Theory of Constraints: a system has one binding constraint at a time, and only work on that constraint improves the whole. Improving anything else is a local optimum. moves the needle, and only until the constraint jumps to the next stage.

The pipeline
items per
18items / week

The whole line sustains only what Code review can push through — the constraint. Everything else is 46 items/week of idle capacity behind it.

22 items/week idle · 45% used
constraint — 100% busy
10 items/week idle · 64% used
14 items/week idle · 56% used
18throughput / week
46idle capacity
61%line balanceThroughput the line sustains divided by the total capacity it pays for. A perfectly balanced line is 100%; the gap is what the constraint forces everyone else to waste.
Lift the constraint
invest in
32.2
20
010203040now

Code review capacity →

Code review is the constraint, so every item of capacity you add here lifts the whole line's throughput one-for-one — until it reaches 28 items/week, where the next-slowest stage takes over as the constraint and further investment here stops paying.
throughput = the slowest stage · improving anything else is a local optimum