Almost every back anatomy diagram I see draws a giant trapezius muscle across the upper back. I work out frequently and I would say (for my body type/size) I have rather large "upper" traps, but have always wondered about the "lower" parts.
It looks like they are always primarily mentioned in the context of scapular "depression". However, I have never "isolated" or purposefully tried to train "lower traps", nor do I feel any "weakness" when trying to depress my scapula manually or when doing exercises (such as weighted dips or pullups) that would make use of any scapular-depression musculature. In other words, I feel no "weakness" in my lower traps when doing exercises involving scapular depression or that seemingly would invoke lower traps for scapular depression or stabilization.
So, are strong lower traps really that useful for most exercises? Do they need to be isolated, or are they pretty well invoked in any exercises involving traps anyway? It seems to me like whatever weaknesses one may have in exercises -- such as dips and pullups -- that should make the most use of scapular depression musculature, the trapezius in general seems like the least likely muscle one would commonly need to strengthen in order to progress in those exercises.