If you need to provide ethernet service directly to a switch, for example something that needs to work even if access to the controllers is lost and the AP goes dead, this would be a good use for the PT port. Basically it is there so you do not have to have an extra face plate for such a port. The -H APs are meant to be mounted to a wallbox where you already had faceplate, and that's why they come with the bracket.
We bought a bunch of RJ-45 dust covers and plugged up the PT ports because we weren't using them, and that way there are less calls to the help desk by people who don't bother trying the other two connectors.