Okay.  I know that the STAR/TRANS part of the FMC, doesn't always (almost never) work in the Captaim Sim 757, and 767, which is very annoying. The work around doesn't always work either, but it works most of the time for me, and sometimes it takes a lot of attempts to get it to work (sometimes I even give up).

However, if you use the ATC for an IFR flight, which is when the ATC guides your flight, once you get on your route, and altitude, everything is fine until you arrive near your destination. Once that happens, the ATC gives you altitude, heading, and eventully a runway that you will land on. It will not follow the STAR/TRANS that you might enter into a flight plan, so why bother adding it. Also, the ATC doesn't care when the FMC tells you it's time to descend, the ATC will tell you to descend when it determines that it's time to do so. So if you're using the ATC for guidance (IFR), I don't see the point of adding a SID, or STAR/TRANS to a flight because the ATC doesn't guide you by them. I never use SIDs, or STARs when doing an IFR flight, guided by the ATC.