In order to grow your account needs followers who constantly engage with your content. Unfortunately, some part of your followers will be bots — profile who are not active on Instagram, meant only to follow, like or comment your account just once for the sake of mutual reaction. Deleting bots from you account will increase your engagement rate (since there will be only users who are actually engaged). Accounts with high engagement rate are more noticeable for users, so it gets easier to get more followers. You can learn more about bots here
makes searching and deleting bots much easier: it has an algorithm which utilizes more than 10 factors to scan you followers for bots. Than he provides you with the list of bots — you can go through it and delete whoever you want.