If you mark in a port some other port as conflicts, pkg does not handle this.
This makes it possible to have conflicting ports installed which e.g. overwrite file on runtime of these application.
One example is www/gitlab-ce and devel/gitolite.
Both of them are writing to a file /usr/local/git/.ssh/authorized_keys if the application is used.
As this conflict happens at runtime it is crucial that pkg respect the CONFLICT defitintion while installing packages.
pkg does automatically figure out those conflict making CONFLICT_INSTALL useless.
There is no need to do anything but let pkg figure it out
I think what mfechner@ means is the conflict happens at the run time, not during the install time so pkg will not know about it. Having a way to manually mark the ports conflict (carefully) might be a good idea.
For those two ports, they only conflict if you try to use them at the same time, which nobody will.