The “micro” in micro-framework means Flask aims to keep the core simple but extensible. Flask won’t make many decisions for you, such as what database to use, and the decisions that it does make are easy to change. Everything is up to you, so that Flask can be everything you need and nothing you don’t.
The community supports a rich ecosystem of extensions to make your application more powerful and even easier to develop. As your project grows you are free to make the design decisions appropriate for your requirements.