It kin of depends on the layout and makeup of the model.. here's an extract from the readme file for my plugin... "...just as background, it doesn't adversely affect anything to change the 'order' facets are listed in the .obj file (unlike vertex ordering, which can redefine things to the extent that may break things like morph files). There are a couple of reasons that you might want to sort them differently, and most of them have to do with aesthetics (.obj files are human-readable ASCII text files) or file-size, but may also be relevant for application implementers who prefer a particular ordering. When you start adding group and material information to a .obj file, anytime a facet (polygon) belongs to a different group, material or region, you have to write out a new record before the facet record. So you can imagine that if you have a humanoid model with 50+ groups and a dozen or so materials, if you just start writing out facets based on the order they may have been created in C4D, you might constantly be writing out a new group or material record every few lines as the list meanders around through the mesh. Generally, you can produce a smaller (and more human-readable) file by sorting them by Group (if there's more groups than materials) or by Material (if there's more materials than groups). Just as an aside, you can still sort by Group, Material or Region, even if you're not exporting that particular record type (though it may or may not ultimately be non-meaningful to do so ;)."

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