Traditional software tuning focuses on finding and tuning hot spots, the 10% of the code in which a program spends 90% of its time. Pipeline tuning uses a different approach: it looks for bottlenecks, overloaded stages that are holding up other processes.
At any time, one stage of the pipeline is the bottleneck. Reducing the time spent in the bottleneck is the best way to improve performance. Conversely, doing work that further narrows the bottleneck, or that creates a new bottleneck somewhere else, will further degrade performance. If different parts of the hardware are responsible for different parts of the pipeline, the workload can be increased at other parts of the pipeline without degrading performance, as long as that part does not become a new bottleneck. In this way, an application can sometimes be altered to draw a higher-quality image with no performance degradation.
Different programs stress different parts of the pipeline, so it's important to understand which elements in the graphics pipeline are the bottlenecks for your program.
Note that in a software implementation, all the work is done on the host CPU. As a result, it doesn't make sense to increase the work in the geometry pipeline if rasterization is the bottleneck: you'd be increasing the work for the CPU and decreasing performance.