In addition to extreme downhill MTB riders, a dropper can also be useful for casual riders who want full leg extension for maximum pedaling efficiency. In this case, the seat is often raised too high to be able to put both feet safely on the ground when you stop. Pedaling efficiency isn't that important with an e-bike since the motor compensates for some efficiency loss.
Some casual e-bike riders, including myself, sacrifice some pedal efficiency and keep their seats set a bit lower to increase stability when stopping & starting. Under these conditions, a dropper is only marginally useful. A dropper also means you can't use a suspension seatpost which, to me anyway, is a necessity. There are combination dropper/suspension seat posts available but I have yet to find one that performs both functions well.
The answer to your question really depends on personal preference, your riding style and how & where you ride. If you want full leg extension when you pedal, are concerned about safety when stopping & starting and can do without a suspension seat post, you might find a dropper useful.