BC sets in SAP PM

Dear Experts

Could someone throw insights into how BC sets can be used in Plant Maintenance module?

In a project I was creating a LSMW for planning plant to planner group mapping as I had 15000 mappings. This is when someone suggested me the use of BC sets.

Kindly share some insights into how a BC set works and pls share the purpose if someone has used it.

Thanks in advance for the help.