Retopology question?

Saw couple of retopo tutorials on YouTube.

My question is why they can’t just use pre-sculpted and sub-surfed ( 1 division) mesh as low-poly mesh?

Why do they have to go though such a trouble to retopo?


Moved from “General Forums > Blender and CG Discussions” to “Support > Modeling”

Because sculpted and subsurf results in a high poly model which is what they are trying to avoid. They want a much lower poly mesh which takes less computer power to animate, often for games where there can be many things on screen at once that need optimising for the best performance.
It also allows control of the topology, where the edges go, providing more mesh detail in areas which will deform for animation (mouth, shoulder, elbows…)
All the smaller details lost in the retopo will be later copied, ‘baked’, across from the original to a texture type called a Normal Map which does a good job of faking small details.