Why the Temples are built on the

 hills and also on the hillocks. ?

The Nature has infinite power, which it is

 positive and negative to the man and  he

  can utilize the positiveness  to some

 extent for the comfortable  liveliness.

 But the nature has the Calamity in the

 form of five elements like Pancha Bhutas.

But the  man knows  his

capacity which a very very  little. 

He seeks  the protection  from

 the nature’s  annihilation.

So for that he prays to the God and 

he  forms the temples in the form of

 Idols on the hills and the small hills.

 When the natural destructions happen ,

 then the man enters  the temples

on the hills  and protect themselves

(him and his family and others)  and pray the God.

Also there can be found absolute silence on the hills.

Hence, the benefit of constructing the

 temples on the hills are mainly for that reason.