Hi Hari,
Follow Function in SAP GTS system is used at times when we have released a particular block at the SAP GTS end and now we want to carry on with our processing for corresponding Feeder system documents.
If you set a follow on Function and manually releases a GTS document Block, then an index will be copied to the Logistics system to be processed at latter time automatically to release a block on the corresponding feeder system document and carry on with its further processing. This is used in the case of Sales Order, Deliveries and Purchase order blocks. Also, this is mostly valid for Compliance Blocks.
I hope you got it now.
In case of any further queries, please let me know it.
Regards,
Aman