What is the purpose of PROCESS_INSTANCE in TL_EMPL_DATA?

We have a customized termination process that runs nightly.

There's a new requirement to inactivate the time reporter data as well when an employee is terminated/retired. Hence, we plan on modifying the customized process and track the process instance of the scheduled process in the process_instance of tl_empl_data.

Another option is to use T&L Auto Enrollment. But TL_ETR_THRED process would not track the process instance in tl_empl_data.

So, we would like to know the purpose of process_instance in tl_empl_data.

Thanks in advance.