When the door is open, the threshold seal is in the up position so it will clear the carpet. When you close the door, the pin contacts the jamb and the seal drops down to seal on the threshold.

From the bathroom side, you want to see tile disappear under the door, from the hallway side, you don’t want to see tile if the hallway is hardwood or carpet. It’s OK to see the threshold but ...

If you're planning to replace the flooring material at the door, it would be a good idea to replace the threshold to prevent uneven surfaces after layers of old flooring have been removed.