What is the difference between USOBX_C and USOBT_C?

The table USOBX_C defines which authorization checks are to be performed within a transaction and which not (despite authority-check command programmed ). This table also determines which authorization checks are maintained in the Profile Generator.
The table USOBT_C  defines for each transaction and for each authorization object which default values an authorization created from the authorization object should have in the Profile Generator.