Saving weight is often a factor when deciding to design and make something out of plastics rather than another material. If something is lighter it is not only easier for a human to carry but also helps to keep transportation costs as low as possible for distribution companies.
The Olivetti Valentine typewriter (1) has a plastic body and cover creating a comparatively lighter machine than its metal counterparts making it a truly portable devise and a precursor to the notion of being able to work anywhere as exploited by laptops and handheld communications devices.
The reduction in weight of packaging material means that transporting products becomes much less costly. By replacing the Celebrations tin with a plastic tub (2) Mars has reduced the overall weight by 46% achieving a 720 tonne yearly saving in material. The reduction in transportation costs can also be achieved by making the packaging materials thinner (3), it also reduces the over reliance on raw materials.