that´s a choice of taste. but with hires chars I also stick to polys. i use nurbs just for technical stuff.
What I meant by depth, is that is based on ones perception.
from this point of view you could also use a front pic and dump the side_ref or even use no reference at all and just watch the model and bring your perceptions to paper.
but - the more reference you use, the better the model.
everything starts and ends in the right place at the right time.