In the manual:
TANGENT
Calculates the u tangents for the 3rd texture coordinate set (TEXCOORD2). This has the same effect as defining matTangent in a shader, and allows shaders to convert vectors to tangent space. The binormal vector (v tangent) can be calculated by the vertex shader from the cross product of the vertex normal and the u tangent. On animated models the tangents need to be recalculated every frame, affecting the frame rate, so don't use this flag unnecessarily.
So, do the models which are animated by GPU bones shader need to be recalculated every frame too?
