Littco
If we have empty legs below RVSM we will sometimes fly the whole flight manually as its good practice!
If I have a low time FO it's a good time to give him hands on experience or some training!
Both these pilots were highly experienced so not the case of a private owner in the right seat having a go )
My jets are 2 crew and we don't have owners ( PAX ) up front but in my twin piston days single pilot yes
Pace