why preferences are asked in upsc ias mains form?

sir i wanted to ask why preferences are asked in mains form when state cadres are allotted purely on the basis of roster system.....pls help.


In mains form they want to know your preferences for the jobs.

fill it till last if you dont want to miss a seat in the ship.

Further they want to know whether you are interested in your home cadre ...
If your reply is no - its negative sign.