EtherCAT PDOs are transmitted cyclically in a fixed length. The standard set of PDO can be sent every Millisecond (1000 Hz). The set of PDO can be customized for two reasons:
A reduced set of objects can be sent faster, hence increasing the frequency.
Some objects that are not included in the standard set may be important for the user (this could include additional information from internal states)
Mappings can also be added for different drives.