This is entirely true if you were a real life company as well. You would want to know how much your or your employees time is being spent and what you or they are producing as a result. For this information, you as an owner wouldn't turn to the accounting department, you would perhaps go ask HR. If you read a set of financial statements they won't tell you the labor productivity of the workers, as investors don't really care about anything other than Salary Costs, and how they affect the bottom line. These are supposed to be Financial only, and not all-informative of in game progress.
Because everyone's time is of a different value, it is usually a bit of a mixture of how much time:profit and time:enjoyment. I thought to measure time to productivity before, but I think the best measurement is when you have finished said task and see how much you sold said product for, just to ask yourself if it was worth it and it should be pretty apparent. For example, if you just sold a batch of sugar cane, the answer is clearly no.