So what are the solutions?

Adding thin edging polygons works, but that's not always the best choice.

Splitting the vertices works every time and costs very little if you do it only where you need a crease. Extra vertices are not expensive - polygons are. And, in fact, welded polygons are more expensive to render than unwelded polygons. So the net result of splitting vertices is a performance increase in all cases.

The third option, though more complicated, is the most sophisticated and optimal. Set up different smoothing groups. Poser will treat adjacent polygons in different groups as if they were not welded. This solution produces the smallest memory footprint, and the highest performance.

But this technique is only for sophisticated modelers and not required for your typical models, like a chair or a low-poly gun.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)