This will impede your ability to excel at pull-ups for several reasons.
As I talk about all the time, when you are performing pull-ups, you need to initiate the movement with your shoulder blades, not your arms.
When your hands are placed too close together, this prevents proper scapular movement from occurring, and leads you to overuse your arms (or other parts of your body) to execute the movement.
One client of mine was even leading the movement with her neck as her hand width was too narrow. The second I corrected this mistake, she was able to perform the movement correctly.
Hand width matters.
A properly performed pull-up is initiated by engaging the muscles of the mid and upper back and drawing the shoulder blades in towards the spine and down towards the opposite hip, not by pulling with the arms.
The second reason why you don’t want to place your hands so they are too close together is because it increases the distance your body has to travel to the bar.
You want your path to the bar to be as short and efficient as possible.
As a general rule, I like to position the hands so they are just outside of shoulder width apart, but figure out what works and feels the best for you.
Just avoid going inside of shoulder width apart.
Also, avoid going too wide as doing so prevents many people from being able to control the movement of their shoulder blades.
You will thank me. And not to plug my pull-up program, but it’s pretty awesome and addresses this error, and many more.