It made the headlines in 2017 and sort of became a meme, but in practice, indiscriminately avoiding left turns in routing can lead to huge inefficiencies.

In my city, trying to avoid one left turn may mean taking 3-4 block detour due to one-way streets. It may decrease fuel usage, but it increases delivery time, and if I'm not mistaken, for most carriers, driver time costs more than price of fuel.