Go if you have two weeks or more, you have been to Morocco before or you are unusually unbothered by rough roads and basic beds, and what you want from travel is to be somewhere that is not arranged for you. On those terms it is one of the most remarkable things in the country.
Don't go if this is a ten-day first trip. The detour costs you two or three days you would otherwise spend on Fes, the Sahara and Marrakech, and the plateau is not a polished experience — there is no interpretive centre, no seating, no schedule pinned to a wall. I would rather tell you that now than have you arrive expecting a festival in the European sense.
There is also a middle path most clients end up taking: come to the plateau in June or September for the landscape, the lakes, Agoudal and the Ait Bougmaz valley, without the moussem. Fewer people, the same country, and the roads at their best.