If you're used to working with a monolithic kernel like Linux or Windows, you might be inclined to start all your drivers before you start any applications. But with a microkernel OS, you have more flexibility and can reorder some of your startup program to take advantage of any idle time. That includes starting applications before starting drivers, wherever it makes sense. In addition, you can use SLM to manage utilitites and services that can be started later or as needed.
A good example of this is the network driver. While the HMI needs the network stack (io-pkt) to be up, it doesn't necessarily need the network device driver to be loaded or network connectivity to be established, so the HMI is launched without waiting for the network driver. Although some applicatiions will need this, only those apps, and not the whole HMI, should have to wait.