Confusion between `kickstart _kernel_custom_options` in addition to `kernelcmd`?

Starting with Foreman 3.6, the new variable kickstart_kernel_custom_options was added (via Feature #35969: Add custom boot arguments for kickstart hosts - Foreman ) for passing in kernel commandline parameters to Kickstart hosts.

Previously, there was kernelcmd which becomes part of the templates via the utility function pxe_kernel_options (which still seem to be used in the templates), which is supported both in Preseed and Kickstart templates.

Other relevant data:
As a Foreman user, I am confused: Is there documentation available on which parameter is suitable for which use cases? At first glance, it seemed that kernelcmd covers all possible use cases, while kickstart_kernel_custom_options only works for kickstart hosts.