Hello @balu504,
Welcome to the Community!
It’s a very good question
In almost every scenario Orchestrator is useful. Especially for unattended robots. Orchestrator allows you to make robots work independently with use of RDP connection. Additionally you can keep crucial variables like passwords or input arguments separately in Orchestrator and have possibility to change them without editing and opening the project. Please visit our LVL2 - Orchestrator Training in Academy. It will help you to understand the functionality.
Additionaly please check our official documentation here.
It depends of your workflow specific. For example without Orchestrator you will be not able to make project where unattended robot will log into windows via RDP. Additionally it will need someone to log the session so robot will be able to perform workflow. I would say that unattended robot without orchestrator is very limited. Please also remember without orchestrator you will have no possibility to manage those 5 robots from one place. This mean that each robot will need to be managed manually on computer where license for particular robot was placed. With orchestrator you have one centralized place where you can connect/disconnect robots, divide tasks, schedule tasks etc.
With your free community edition license you get 2 robots for free. Like Pablito mentioned there’s a lot of things you can do. I love to schedule my robots in Orchestrator to have them run on it’s own. If you need more than 2 robots, yes you will need to buy a license.