Flutter is used when you need to create an MVP in the shortest possible time - a minimum viable product. With this set of tools, development is about twice as fast. For convenient and fast work, there is a Hot Reload function, with which you can instantly view all changes in the code without losing the current version.
Due to its simplicity and convenience, Flutter will become the most popular tool for creating mobile applications in the near future.
Google is actively promoting its technology, while React Native is gradually losing ground. Both technologies so far hold very high positions on GitHub: 113K stars (Flutter) and 93K (React Native), and in 2020 Google development took the lead for the first time.
Another advantage of Flutter is the lack of improvements from the past. Most popular development tools have been around for a long time, so they contain old methods and technologies that need to be constantly improved. For example, Xamarin was written in 2011, and Flutter was written in 2017, which makes its methods more modern and simpler.
The young platform also has disadvantages: if problems arise during development, then most likely it will not be possible to find their solution on the Internet. Flutter is a new tool that hasn't been worked with much yet. Probably, with the growing popularity of the framework, this shortcoming will disappear naturally.