Question: Lot of questions has been already asked about the differences between string and string builder and most of the people suggest that string builder is faster than string. I am curious to know if string builder is too good so why string is there? Moreover, can some body give me an example where string will be more usefull than string builder?

Answer: 
StringBuilder is better when you need to change the value. Otherwise, there's no need for it.

If I need to use the same string value in 10 places, as it is, I'll use String. If I need to change it 10 times, StringBuilder.
In brief, it's a trade-off between **mutable** and **immutable**

See this:[StringBuilder vs String](http://channel9.msdn.com/forums/TechOff/14294-C-string-vs-StringBuilder/)