1. What are the uses of creating multiple actions by virtual user script(v user script)?

Advantages are Reusability, repeatability, reliability.
Also if the code in load runner goes beyond 1 lack lines, we get a compiler error, so we need to split the code into multiple actions.

If we split the code into actions, it will be easy to do any modifications if needed.
Ex: login action, delete action, credit card processing, etc