@kpa:
I agree that the checkmark should have the same function regardless of the interface type, be it enabling/disabling the interface completely or just enabling filtering/NAT on the interface. Neither the GUI or the existing documentation give you any hints of different semantics of the checkmark's function depending on the type of interface now.
On Reddit I discussed in more detail other problems of the "pfSense Interfaces" architecture, such as different meanings of "IPvX Configuration Type" depending on the corresponding FreeBSD interface and on the selected field value itself.
Right now pretty much nothing is consistent, it's a bunch of hacks to make common (and less than common to some extent) scenarios work.
I hope they will fix it soon. It is, imho, one of the worst downsides of pfSense in comparison with major commercial solutions (e.g. Cisco).