Found this while trying to create an observable plot with multiple scales[1][2].
I'd argue multiple scales are OK if the multiple axes have different units that can't be easily compared/confused and are used for greater information density (instead of relative comparison purposes).
For example: I'd like to plot weather stats like hourly temperature, precipitation, and AQI throughout the day, so several different days can be compared with each other. (And fit all this information on a mobile screen.)