GPS/FMS units are only helpful for situational awareness if you keep the pink line in front of you. As soon as it is behind you, the GPS is helping you set up perfectly for messing up. What I am referring to is making sure that the Active Leg on your GPS/FMS unit is actually the leg you are on. This will involve some monitoring on your behalf. For example if you load an approach into your GPS and include all of the fixes along the approach your in great shape. That is until ATC gives you a short approach and vectors you in tight just a mile or two outside the Final Approach Fix or Point. You have to be sure to always clean up your box and activate the leg you are on. It especially on an approach to have your active leg behind you. In the case of a missed approach you will get confused and end up having to do a bunch more steps in your GPS system to figure it out.
Just remember, always keep the pink line in front of you!