Back training is very important for the following reasons:
1. It adds to side-view thickness.
2. It enhances the all-important V-taper.
3. It creates muscle balance with chest musculature.
4. It gives the body a symmetrical appearance
5. It prevents shoulder impingement issues by playing an integral role in preventing forward shoulder.
The keys to developing an awesome back are shrugs, rows, and pull-ups. Good trap development comes from heavy barbell shrugs and the indirect effect of overhead shoulder presses and upright rows. However, to directly stimulate the traps for mass and to develop shoulder thickness, one needs to shrug heavy at times and at other times, shrug for the "feel."
I like to do traps with back training. For my back day, I train my mid-back mainly and the two key priorities in my back days are lat width and upper-mid back definition. Find what works best for you, however don't over-complicate things, keep it simple.
Richard-