And I assume that'll be the same for destination. If I want to fly my flight plan as published in the FMC, I would enable STARS and set the ST but if I want the vectors from ATC, disable that.
It's a bit different for the destination because the ST designation and the STARs box are really two different things. The STARs box is very specific and applies to the last waypoint in your flight plan. If unchecked, you get vectors from your last waypoint to the airport. If checked, you do not get vectors after the last waypoint. You are cleared at pilot's discretion for approach to the active runway and need to get there on your own (by hand, or by any procedure you want, with or without your FMC).
The ST designation is optional. You can use it if you want PF3 to issue you a STAR clearance at a waypoint other than your last waypoint, but it really does not affect the flight as you are still expected to follow the rest of your flight plan and the ATC behaviour at the last waypoint is still controlled by the STARs box.
TIP: If you think you may want vectors for landing, do not check the STARs box before the flight. When ATC starts vectoring you at the last waypoint, you can always use Hotkey 1 to request clearance at pilot's discretion if you decide you don't want vectors and would rather fly the approach on your own.