There are two main benefits from performing the band pull aparts.
Many of us have terrible postures do to staring at our phones or sitting at our desks all day. This can lead to shoulder, lower back and neck strain.
The band pull aparts reverses the effects of the bad posture, by strengthening the muscles that help keep us upright.
Band pull apart leads to healthier posture and strengthens the stabiliziers that control the shoulder joint.
As we know, bad posture and weak stabilziiers often lead to injuries.
You can imagine that the opposite will reduce and prevent injuries.
Increase Pulling Strength
When performing pulling movements, the rear delts are being used. However they never truly get trained to failure since its not the primary focus of most pulling exercises. Therefore is never gets trained to its full capacity.
A small muscle lke the rear delts really needs high frequency and training to failure to grow optimally. Pull Aparts encourage more hypertrophy.
Given two identical people, except that one has more developed rear delts, who do you think will be better at pullups and rows?
It may not be a big difference but it's most likely noticable that the one with better rear delts will pull better.