The main appeal of App Selector is the flexibility it offers. You can choose which apps you want to use for different tasks, and you can even set multiple apps as defaults for the same task. This means you can switch between different apps depending on your needs.
This feature is especially useful if you have multiple apps that can perform the same task. For example, if you have multiple music players, you can set one as the default for playing music files and another as the default for streaming music.
App Selector Android: What It Is + How To Disable It - YouTube