The plastic is just one possible application.

The important part is the conversion of CO2 into carbon monoxide and ethylene.

From ethylene and carbon monoxide a lot of useful organic compounds can be synthesized. One could make synthetic gasoline for vehicles, or one could make glycerol and use it to feed a culture of fungi for producing cheap protein.

The world is dependent on plastic by now, and needs a lot of it. The negative stigma it got lately is due to playing fast and loose with it in the past, but it is a necessary class of materials, and having sustainable means of mass producing it is a good thing.