What is the difference between span-by-span construction and progressive placement?

Balanced cantilever construction simply cantilevers segments from a pier in a balanced manner on each side until the mid-span is reached and a closure is made with a previous half span cantilever from the preceding
pier.

Progressive placement is similar to span-by-span construction as they both start from one end of structure to another. In progressive placement, precast segments are progressively placed in successive cantilevers on
the same side of the same pier. This differs from the span-by-span method in which segments are cast at alternative sides of the same pier such that the hogging moment at the pier is counterbalanced. For progressive placement, temporary stays with temporary tower are placed on the pier to limit the cantilever stresses and deflections.

This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.