Compostable packaging vs. lightweighting packaging

A lot of packaging on the supermarket shelves is overweight. Lightweighting this packaging is one solution to reducing packaging waste. However should there be more focus on developing packaging that is 100% biodegradable and compostable. The question we ask is;

Is it more environmentally friendly to use compostable packaging or to lightweight packaging that ultimately goes to landfill?

Reduce packaging waste going to landfill

Many large manufacturing companies are setting targets to reduce landfill. The question we ask is;
How do you know whether your targets are achievable or even sensible?