Best Of

It's a case of "it depends".

Here on UE5 Manny (top), the transition from soft parts to hard panels is continious, achieved with a very precise placement of loops perfectly following the transition (and therefore also dictating the ID/texturing mask, which ends up being nearly per-polygon hence very clean and robust). Yet on McGinnis from Deadlock (bottom) the forearm is shoved into the glove and parts of the glove itself are shoved into each other, which is a somewhat unusual practice but has some advantages.

Neither of these two scenarios is dicated by "saving polygons".

Being wasteful is of course never a good idea but that's not the deciding factor for this kind of stuff and it has not been the case for about two decades (in the sense that keeping or deleting a few hundred tris keeps a model within the same order of magnitude density-wise anyways, hence would likely not blow up a tech budget). What matters is the actual context the model is used in game, the way it behaves in motion (with no way to hide things per-shot or in post ), the desired visual art style, and even to an extent the shading/rendering style.

For instance had Epic decided to have the hard shell panels float on top of a soft bodysuit underneath, this would mean a significant chance for some unintend clipping and interpenetration creeping in under extreme poses especially with third-party animations from the marketplace ; and their LOD generation might also have been compromized. Yet Valve had some different constraints driving their decision of shoving parts into each other, the main one being probably ease of editing since their setup allows for later adjustements to the ingame model without any rebaking, whereas any edit done to the Epic UE5 mannequin would naturally require a complete rebake with new UVs.

At the end of the day the final ingame model is the only thing that really matters. It dictates everything, including the way the highres model is built. This is less true for portfolio pieces but very much central for any production model.