Summary:
Mobs on placed in the air scaffolding will not move "unnecessarily". They will move if the player takes a treat in his hand or if one mob attacks another. But just walking and when burning mobs will not run and walk. This does not apply to scaffolds placed on full blocks.

Steps to reproduce:

1. Place the scaffolding platform in the air.
2. Summon a couple of mobs on them.
3. Observe the behavior of the mobs.

Observed results:
Mobs sometimes cannot find their way on airborne scaffolding, which is why they will often just stand still and not move.

Expected results:
Mobs will move on scaffolding like full blocks.

Image: