I am working with switches, wireless, and SD-WAN solutions, but regarding the opinion itself, it depends what one would like to get.
For what we do, the most useful feature in Cisco Identity Services Engine (ISE) is RADIUS authentication. We are using the guest portal as well, the Wi-Fi guest portal capability from Cisco Identity Services Engine (ISE).
The Wi-Fi guest portal feature allows us to give access to non-company devices on the locations we have for visitors.
We use the Cisco Identity Services Engine (ISE) profiling feature to onboard new devices whenever they're connected and assign them the correct profiles. It was mostly used when the ISE was deployed, but it's still used.
The adaptability of Cisco Identity Services Engine (ISE) policy enforcement can fit to the site we have depending on which kind of devices we have on site and then the needs for authentication, granting access and then assigning each device into its correct network for segmentation.
For what we're doing so far, it's quite easy for us; we are not doing too much complicated stuff, so it's quite easy for us to onboard a new site into the current policy we have.