MicroKernels act as persistence managers starting from AEM 6.2. Choosing one to fit your needs depends on the purpose of your instance and the deployment type you are considering.
The below examples are meant to be an indication of what are their recommended uses in the most common AEM setups.
Single TarMK Instance
In this scenario, a single TarMK instance runs on a single server.
This is the default deployment for author instances.