relationship ? b/w tables

Question

Hi

 

 Well i am confused on this issue . I hope some gives me required clarification

 

There are two tables lets say A,B or  whatver it may be  with primary keys & foriegn keys  ,

 

Is it necessary to give the relationship b/w tables  there in sqlserver managment studio itself ?? ?? whats the use ??

 

I used to write simply join statements or not or whatever  to fetch data b/w tables but i never created a relationship there at database level on TABLES ..

 

Why do we do so ? is it manditory ? i know one advantage i.e we cant delete a parent table it is under relation-ship :)

 

Any more suggestions /

 

Regards