INITTRANS can be allocated for a table based on the following criteria:

the space you would like to reserve for transaction entries on the table
the number of concurrent transactions that access the same table at any given time

For example, if a table is very large and only a small number of users simultaneously access the table, then, INITRANS can be kept low.

On the other hand, if a table is accessed by multiple users at the same time. use a high INITRANS