Doctors/Nurses... Normal Saline question?

I've noticed that normal saline is used for a lot of things. Its sometimes given IM, used to clean wounds, inserted nasally for congestion problems, etc. What is it about normal saline that makes it useful for all types of procedures? Is it the same as NaCl? Just how does it help regarding giving it IV in cases of dehydration? Why would they give NS vs D5W or any other fluid?