1. indivisibilities - photocopier.
2. Specialisation - A. Smith - you do what you are the best at and learning by doing.
3. Physical economies (double the size, volume goes up by 4 times)
4. Financial economies (buying bulk, not a saving to an economy). There are co-ordination problems.
The efficient input path is only valid in Lr, in Sr you can only vary labour. So you keep capital horisontal and move in an horisantal line.