Originally Posted by Hohenheim of Light
You don't need to, necessarily. Isolation exercises are like simple carbs i.e. only do them if you think you deserve it. Most compound lifts will work your entire arms anyway, especially the biceps and triceps. If anything, deltoids deserve a little more attention but if you're like me and your deltoids are naturally big, then that won't be needed either.
Maximum amount of GHRH is released during Squats and Deadlifts, working the biggest muscles together. This is what stimulates the growth for the arms as well. Focus the majority of your training on the big muscle groups. The smaller ones will adapt to accommodate the strain.
You got it dead on my friend.