Sometimes I use a TRANS that is listed under the selected STAR (left side of the CDU), other times I select the TRANS under the RWY (right side od the CDU), and sometimes I use both. But I always try to use a TRANS. If I don't use a TRANS, the flight plan doesn't show the end of the route at the runway or a holding point after the runway. It usually ends at the last waypoint of the STAR. This is not a big deal because if you are close to the ILS you can still capture it, although you might find that you will need to enter the ILS frequency and heading manually (RAD/NAV page of the CDU).

Mark