Target costing is all about keeping costs at a particular level so that profit margins can be maintained at a particular selling price.
This can be done through efficiency, redesign, automation, reduction in quality or sometimes reduction in quantity.
Usually when a company reduces the quantity of product it sells for the same price it gets away with it. for Toblerone, the new design and reduction in chocolate was a bit too obvious.
http://www.bbc.co.uk/news/uk-37904703
