I love multiple exposures. I used to figure out equations and exposure times back in the day with film cameras, but now all you do with a Nikon body is go to the shooting menu, choose multiple exposure, set the number of frames and shoot away. The camera figures out the exposure and seamlessly puts the images together. On workshops I often talk about creative effects using multiple exposure such as twisting the camera during a shot to get a really abstract image. But recently someone asked me is there a really good reason to use multiple exposure without creating wild abstract shots. My response; I use multiple exposure when I only have only speedlight to illuminate large scenes.
Take the image at top as an example. This old car just begged to have the interior cab lit using a speedlight. But if the interior was lit, the shot would look better if I used a flash on the exterior as well. Since I only had one speedlight, I did a double exposure. I set up my camera on a tripod, set the camera for a 2 shot multiple exposure, and took the first shot with the speedlight in the cab. Next, I went over and got my speedlight out of the cab and aimed it at the exterior for the second shot in the double exposure. The final image looks like it was lit by two speedlights at once, but really it was one light used twice in a double exposure. I have lit hotel interiors doing 3 and 4 shot multiple exposures, each time moving the speedlight during the multiple exposure. This technique works great on a tripod with static subjects. Moving subject or camera shake will cause ghosting in a multiple exposure. By the way, the new radio controlled SB5000 (with D500) allowed me to place it out of sight in the cab and still trigger it from the camera without any signal issues. Loving the new radio controlled SB5000!