I really do not see a savings in gas mileage great enough to justify the cost of LED lights especially with the high HP motors of today.
Now if you want to put 100 chicken lights on 1 small wire;
Want lights that have several burned out and can still pass a DOT inspection;
Want lights that take a better shock load;
Have lights that lend themselves to replacing the whole lens; bulb; case; when the bulb burns out.
Then maybe you have a use for LED.
LED lights became common on trucks for all the above reasons. Small trailer places use them because that is what is available.
Some car manufactures are even using them now because they look cool.