[jstanley]

Profiling data tells you how much time your software spends running each part of the program.

At the highest level, you might just know "we spent 25% of time reading from the disk, 10% writing to network", etc.

At the lowest level, you can know exactly how many times each instruction was executed, and how long it took, and the call stack of each execution.

Normally somewhere in between. The appropriate level depends on what you're trying to optimise.