Hey,

It's relatively easy for a SC candidate to clear prelims and mains. Prelims seems to be the most unexpected stage of the exam. In prelims 2016 the expected cut off for general merit is around 110 (+ or -2/4) while for SC it is expected to be around 95–100 which is a huge advantage. In mains too SC candidates enjoy huge advantage over GM since the cut off is around 30–40 marks less than GM cut off. Once you clear prelims and mains, the advantage in service allocation is also huge compared to GM candidates. To give you a perspective, there is no GM candidate above around 500 rank. Anyone who gets above around 500 is either SC or OBC. That itself gives one huge psychological advantage.
Having said this clearing UPSC is not cakewalk for SC candidate. Though there is difference in cut offs at all stages of the exam, quality expected from a candidate is still very high. SC candidates will have to work as hard as GM or an OBC since one cannot quantify preparation in terms of marks.



Hope this helps.