Magento 2 offers easy integration to RabbitMQ, but why and when do I need RabbitMQ installed in my store?
Making long history short, you need it when you have to optimize the high load operations in Magento 2.
RabbitMQ is a message broker that primarily uses AMQP for processing communications between 2 applications. It is a middleman where Queues can be defined and applications can connect to the Queues to pull the messages. Some tasks might be time-consuming. There would also be a need to handle multiple requests. The message broker puts these tasks into corresponding queues for the other application to process these independently.
Message Queuing allows web servers to respond quickly to requests and delegate them to a third party for processing rather than perform the task instantaneously. This helps in handling multiple, resource-intensive requests efficiently.
Reference: RabbitMQ Magento 2