For gas engines, but this is about diesel which have very different properties.
Even when talking about gas engines, if you are towing (this is about diesel where towing is more likely than normal) your turbo is running all the time anyway and there is no savings over a bigger turboless engine, and the bigger engine will last longer. The bigger engine can also run at lower rpms which brings up power. In the end for a lightly loaded gas engine a small turbo is more efficient.
Even when talking about gas engines, if you are towing (this is about diesel where towing is more likely than normal) your turbo is running all the time anyway and there is no savings over a bigger turboless engine, and the bigger engine will last longer. The bigger engine can also run at lower rpms which brings up power. In the end for a lightly loaded gas engine a small turbo is more efficient.