On one hand, it is wise to master the numbers and the deeper you look into them, the better off you will be. On the other hand, practical considerations apply. As you gain experience on the road, you will come to understand that always/never rules may not always be best to follow.
For example, after you study Leo's excellent post on fuel taxes, you may decide to never buy fuel in a particular state, even if it is seemingly priced lower on the truck stop signs. But on a particular run, it may happen that the smart move is to buy fuel in that state because you need to top off after a delivery and get quickly to sleep so you can be ready to roll if your next load offer comes quickly in. Or it would be unwise to detour to another state if relocating closer to a busy freight center in unfavorable tax state is the wise choice at the time.
In expediting, you are continually weighing several trade-offs at a time. In that ongoing process, the more you know the numbers, the more often optimal decisions will be made.
When you are a prospective expediter, looking into the business from the outside, the biggest challenge is gaining a sense of perspective. It is easy to run hypothetical scenarios but until you actually get in a truck and experience the day-to-day flow of events, it is difficult to weigh one factor against another because until you get into the truck, you won't truly know how much weight you personally assign to a given thing.
For example, above I talked about fuel purchase in a certain state and preparing for the next load offer. Not mentioned in that scenario are the number of days you have gone without a shower, how close to home you may be, whether a close expediter friend is at that truck stop, what day of the week it may be, how soon your next oil change is due, and many other such items.
Absolutely, get to know the numbers as best as you can. Doing so will give you a decisive edge. Just know that the numbers are only part of the bigger picture of expediting success.