In prefabrication it may make some sense since the parts are to be hauled and put in place with some impacts and this could damage the thing. This is true for columns and piles. Normally coming from prestressing plant and fc being higher for PC parts completes why are so being made, the plant sells more, and in reality remanent compressive strength can be even more than RC...at higher cost, must be.
In some cases the columns can be really tension members and prestress is used withing the column for fire protection etc. I haven't seen it in concrete but exterior prestress is used to this purpose in the inclined steel structure of the KIO towers (or Puerta de Europa).
Other intelligent use I have seen is to equalize the compressive stress at same stories of adjacent and connected tall buildings of different height; this way it is assumed the axial shortening will be equalized along the whole life of the buildings, and stories will remain level.
Yet another reason to prestress a column is to reduce the tendancy of slender columns to buckle. Check out the chapter in T Y Lin on prestressed columns
You can prestress or poststress the concrete columns or beams,the idea is introduce compresion stress in addition to be reduce in case the member is submit at tension. The element follow working in compresion before and after the force are applied.
You can prestress columns to take a temporalily tension state. For example, if you have a high freatic level in a deep foundation, some columns of the building could work like tension members until the weight of the high levels be enough.
Idle when structures must support big gradients of temperature between differents sectors.
Cheers
