trial balance issue

1- i have a company segment its values

    01  x

    02  y

    03  z

     T   total           from 01 to 03

2- i create journal for 01 (for example account 511   value is 100) and post it.

3- i create journal for 02 (for example account 511   value is 300) and post it.

4- when run trial balance for 01 for this account 100

5- when run trial balance for 02 for this account 300

6- when run trial balance for T no data on report

    my first question why no data on report when pass T ?

    what is the advantage of T on balancing segment ?

i try to create summary for t on segment company