The problem is when the cost of the electricity is higher than gasoline, sometimes far higher. This is bizarre in Canada where the gasoline taxes are very high.
I have a hybrid, so I use the cheapest option, but I also see high priced chargers sitting idle.
The pricing methodology is all over the map. A new problem is the practice of free level 2 charging and charging money for fast chargers. The fast chargers sit idle and the free L2 chargers are all in use. Personally, I would pay, but my car only supports L1&L2.