They follow you anywhere and teleport if you use a broom. They cast Lumos and Disillusionment when you do and will Avada Kedavra whoever you want if you download another mod from the creator. Companions can also come to the Room of Requirement and battle arenas with you.
Your helpers are not just sidekicks, there so you don't feel too lonely, they level up together with your character, so you're not going to be too far apart in terms of skills. Khione also added one skill to each companion, so, for example, Professor Garlick uses Chinese Chomping Cabbages and Sebastian wields Petrificus Totalus.
