Hi@AbhishekC1725

First of all Obj-Save is an activity method used to save the object in DB and Save is an OOTB activity provided by Pega to save an instance in the DB.

With Obj-Save you can commit your changes to DB immediately or you can also defer commit based on your requirement. Obj-Save also allows to save the data with errors. On the other hand Save activity is much more better from error handling perspectives. 

In conclusion both Obj-Save method and Save activity achieves the same objective, but the Save activity is much more robust in terms of error handling and saving data to DB.