The Multiple-Exposure feature has been in the semi-pro and pro line of models for quite a while now. I am not too sure if many of the photographers use this feature but I do actually use it when I photograph different genres to create images that look different and have a different flavor to them.
In the Nikon D850 , the mutiple exposure mode has been improved by now giving the photographer the option to save or not to save the individual exposures used to create the multiple-exposure.
This additional option is another excellent initiative by Nikon as it again encourages the photographer to re-look at how he or she can be more creative in using this tool.
For example with the individual images saved , they can now be used to optimize the blending flexibility during post production with the potential to produce even better creations.

A few tips in creating interesting & appealing multiple-exposure images :
1. Try to overlap images with SIMPLE backgrounds where possible
2. As always , PLAN your multiple-exposure shot in your head , PRE-VISUALISE it first
3. Avoid overlapping too much or overlap onto a plain / simple background
4. Executing point 2 & 3 will help in determining where to place the main subject
5. I like to use AVG overlay mode but do experiment the different modes available.
Multiple Exposure (2 shots) Highlights from today's (20th Oct 2017) WTA Future Stars - SemiFinal match between Salsa AHER from India and Ya-Hsin LEE from Taipei.





VERSUS regular tennis action shots which can be a tad "boring" at times


Nikon has not only introduced new cool tools like the FOCUS SHIFT tool to provide more creative imaging options to photographers , Nikon has continued to update & improve existing tools too like the Multiple-Exposure feature.
Great going Nikon !!