The Captain,
Yes, I think you are missing something. Very simple example:
You make $10, you deduct a fuel expense of $3 - you netted $7 and that is what you pay income tax on.
The fact is you paid $3 for fuel out of your pocket. You used it as a 100% expense and you didn't pay income tax on that money you brought in, but you still bought the fuel using your money. If you can get the fuel at a discount, get a rebate on it, or not pay road tax on it, then it is money in your pocket - lower expenses.
Some of the fellows have mentioned that certain States allow you to claim back the road tax on gasoline that was used in off-road equipment. It is simply a matter of tracking your purchases and making a claim at the end of the year. This can add up to a tidy sum.
Lower expenses = more profit.
You are definitely missing out.
deej