I’m 90% positive that I did this because my skeletal meshes are stitched together from different sub-meshes (body plus clothing, hair and stuff), which all have their own set of double vertices saved as data-assets, so these can be combined by putting pointers to the individual submodel double-arrays (from the data-asset) into an array for any given final franken-mesh. FindDoubles only operates on one “undividable” model at a time. So that’s why, unless my memory is failing me…
So, you can just ignore the outermost array, if you’re doubles don’t need this kind of flexibility.