More smoothing groups or more polies?

Performance & Profiling
1

Greetings, in some engines many smoothing groups mean less performance, this is quote from official CryEngine docs:

Use as few shading groups as possible. Adding a new shading group is often just as expensive as chamfering the edges and using only one shading group because the vertices in the different shading groups will be split and effectively doubled in the engine. Additionally, having chamfered edges in the silhouette helps the shading (they create a highlight) and avoids aliasing issues because a chamfered edge doesn’t look as harsh as just two faces in different shading groups. Also, it looks more natural because most edges aren’t 100% sharp. This needs to be decided on a per asset basis. http://freesdk.crydev.net/display/SDKDOC3/Asset+Guidelines

Does that apply to this engine as well?

2

Different smoothing groups will result in additional vertices which have to be calculated.
However in most cases vertex calculations should not be that expensive, so an optimization of other bottlenecks like fill rate and draw calls is probably more effective.
Maybe if you have expensive per-vertex calculations and a lot of polygons this could be an issue.