Since I first started writing the reply over an hour ago till now and it’s still encoding textures. So my first question is regarding why the building is taking place at all. And the other for why it’s so slow on my mac.
For the second I think I might have found a kind of answer in the source code : TextureDerivedData.cpp (where the encoding happens) starts with a, well, namespace called TextureDerivedDataTimings which seems to be to determine what is taking so long … Though I’m not sure where to see it’s output.
Also, regarding the first about why it keeps happening - It looks like in the source the textures are encoded according to both settings and target platform. So I’m not sure why it keeps happening … Will keep digging …