If that's the sole charging method, then a faster battery degradation is expected. Note that fast charging adds quite a lot of heat. Worst case is starting with a low charge, fast charging, going to a highway, fast charging at the destination. I've only done it once while traveling so I don't think the battery even cared – I still have full bars on a 1.5 year old leaf.

Note that the Leaf's battery is not actively cooled (it does have heaters for extreme cold). So it could be the case that people living in colder climates could get away with it with little degradation.

Still, you should keep quickcharging to 80%.