Is there any reason to use NaN instead of missing?

General Usage
4

Yes, there are lots of performance (type stability) reasons to use NaN!
The overhead with missing can be more than an order of magnitude even in this simple example:

julia> x_nan = [([1., 2., 3.],), ([1., 2., 3., NaN],)]

julia> x_missing = [([1., 2., 3.],), ([1., 2., 3., missing],)]

julia> @btime map(x -> sum.(x), $x_nan)
  35.578 ns (1 allocation: 80 bytes)

julia> @btime map(x -> sum.(x), $x_missing)
  378.745 ns (8 allocations: 240 bytes)
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