Traceability matrix is prepared to check whether all the 
functionality or Usecases covered or not.

With this matrix a lay man can also understand the coverage 
of the testing. ( Like we can easily find out how many test 
cases are passed or failed.)

In real time....
We will prepare this in Requirements TAB in test director,
we will add test cases against the SRS doument/Usecase 
Document.

Still u have any question... Then feel free to send me a 
mail.

Raju,
krishnaraju.m@gmail.com