just bought my SGSP on sunday. a new user of android hp n no nothing about rooting.

1)y should i do rooting to my hp?

2)my hp tend to switch off by itself when it's in my bag.it happened 3 times today,anyone same like my problem?

3)at one time,my friend called me but i only can hear the phone ringing,but no display,as if it is switch off..i dnt understand what happen here,can anyone care to explain?

What is rooting? do i hve to root my hp?pls help..