I’ll explain why this is not necessarily true. If you are able to take home leftovers, there is less incentive not to end up with leftovers. Hence the amount of leftovers should _increase_ as a whole. Some of those leftovers will be left in the restaurant by customer choice (resulting in waste) and some will be taken home. Some of the food taken home will not be eaten which then also will become waste.
So the question as to which system results in less waste boils down to a question that must be answered experimentally.
Reducing waste on a societal level is complex. Cultural practices of restaurants boxing food to take away may result in less waste but it may also result in more waste.
> If you are able to take home leftovers, there is less incentive not to end up with leftovers
I feel that having leftovers is never desiderable, with or without the ability to take them home. In France the restaurants are obligated to allow you to take leftovers home, and in my experience this has not changed anything on the behavior of people eating in restaurants. The only thing that changes is that in the rare case in which you have leftovers, you can take them home.
So the question as to which system results in less waste boils down to a question that must be answered experimentally.
Reducing waste on a societal level is complex. Cultural practices of restaurants boxing food to take away may result in less waste but it may also result in more waste.