How does create trigger checkbox under table build / alter option in App Designer works?

Hi,

I know for many it may be basic question, but I do not get much details in peopletools books, so trying to get answer from PT experts. When we try to build a table in App Designer following screen shot appears. When you look at build options, the last one comes as "create trigger". I am not sure how this option is used internally  to create the trigger.  When you select Alter option, create trigger is automatically selected and disabled, so you cannot uncheck it. If some one can provide great detail on this option would be helpful..

For example, take a table - PL_PROD_OPT (We are using PT 8.55.12 on FSCM 9.2 PI 23) open this table in App Designer and build option. Select only create trigger and generate the build script. You can see it generated a trigger like below. But not all tables generate such scripts.... So would like to know what table properties or options for this table to generate the trigger vs not for other tables