Lifters often can't engage their lats while doing pull-ups. As a result, they may experience elbow pain, tendonitis, and neck pain. To top it off, they'll assume that the pull-up doesn't add size to the back – because in their case, with their form – it won't.
What could be causing this problem? Well, the obvious answer is that the wrong muscles are getting used and the tension is getting placed on the shoulders and arms instead of the back.
The not-so-obvious thing is, when pulling ourselves up, we rely heavily on our grip being at its strongest towards the index and middle fingers, but never really think about how that will impact our shoulder position.
A great coaching cue is to tell people to lift up their index fingers as they perform a set of pull-ups. Not only does this put the shoulders into a better position, it'll also make it infinitely harder for someone to power through with their biceps, which in turn will make them better at pull-ups and give them stronger, bigger lats.
Most people that experience shoulder/arm/neck issues struggle to match their normal max set of pull-ups with the index fingers lifted, so this is a great way to check if you've been using the correct muscles. If you're only one or two reps off that's fine, but if you find your reps are cut in half or you really struggle to do one, then there's room for improvement!
Regardless of your level, I'd recommend always throwing it into your warm-ups for lat/upper body pulling days because it's just a great activation tool. By putting focus on the right muscles, hopefully you'll avoid running into any issues with your pull-ups in the long run. Longevity is the key to consistency.