Originally Posted by gdl203
I really depends on body shape and posture. For some people, the only way to deal with excess cloth in the back without messing up the fit in the front is to add darts.
... specifically, if your drop is larger than average, it is quasi-impossible to create a fitted shirt without darts because there are limits to how curved you can make the side seams; plus, there is the complication of the back being a 3D structure that not only tapers sideways, but inwards (i.e., the z-plane).
in most cases though, one won't need them.