Some lifters have trouble hitting their backs, even with back exercises. Often, the biceps take over. The unilateral lat pulldown allows you to really focus on the back one side at a time.
Do not fully extend the arm at the top of the movement.
This article isn't going to overwhelm you with neuroscience or obscure language. Nope, it's going to be bare-bones simple. As I've learned over the years, elementary advice is usually what helps people most, and it tends to work best.
There's no such thing as isolation in training or in life. Everything you do, have done, and will do, affects everything else. Success is a synergistic – not additive – phenomenon.