Relational Database Service (RDS) is a web service provided by Amazon and most of the company use this service because it is fast, secure and cost-effective component of a modern cloud infrastructure. RDS provides six familiar database engines, including popular open-source options like PostgreSQL, MySQL, MariaDB.
In short, it is a Database as a Service, where Amazon deploys and operates your database. It takes care of tasks like backup and patching the database software, as well as high availability
It’s also easy to get good baseline performance with RDS. Each RDS instance is pre-configured and optimized based on the selected size. RDS instances scale by adjusting DB instance type (memory or compute power up or down) as needed. It’s also simple to configure read replicas or set up synchronous replication across availability zones for enhanced performance, availability, and durability.

Using RDS, the fully managed service option, can be great for removing a majority of DBA tasks. However, the service does not currently provide the option to run every type of task.
RDS also manages replication. If developers need high availability in a database, the multi-availability zone option in RDS can be used. With that option, a replica database is kept in sync with the primary database in case of failure.
Keeping UP with Cost:

“Pay for what you use” you need to keep an eye on what it is you’ve got running on the service. If you are using instance for POC/Testing and you forgotten to terminate it and over-allocation are common causes of spiraling costs.

You can estimate your monthly bill using costings calculator.

Down the line as a small enterprise or medium-sized business good option to bringing the hardware services in-house might make sense. But if the business scaling rapidly or running on a short-term basis, then AWS should continue to be a best option.