I use reference EVERY time
Every Art instructors and tutors recommends using references, especially when you don't know the subject and if you ask yourself if you should have reference.
Before I begin any panel, I lay some references on the drawing itself (next to the area where I draw)
If the environment is new, getting references will take you few minutes and will add a lot to your drawing :ideas on what to put in there, realism ( how weathered is the object) , how the world or object functions (even the simplest things)
even my own previous drawings , so I don't miss things I've put in the location and keep it consistent
I even put my previous drawings as reference (to not forget any things i've put there)
this might be a good start, this profile provide great quality enviro (scroll down) and characters refs
http://pinterest.com/characterdesigh/_saved/