The idea of a spirit who was haunted in life (as the Ghost Host is suggested to have committed suicide) opening up his home to all these other wayward spirits who cannot pass on for some reason and giving them a place to rest and enjoy themselves. He could just as easily have kept to himself.
The film versions' ending, where thanks to the Evers family, all the spirits save Ramsley are freed.
"Angels in Heaven, together at last. The tale is well ended for those who have passed. Love endures all, no reason, no rhyme. It lasts forever and forever all the time."
Ezra and Emma waving goodbye.
The fact that they left with Madame Leota and the Singing Heads.
Since he was such a fan-favorite character, the Imagineers brought back the Hatbox Ghost, with advanced effects that allow him to work! Many fans are overjoyed about his permanent re-addition, and some even claim that he completes the Mansion.
The Ghost Host manages to make one that is also rather creepy. Apparently, all of Constance's husbands still love her, even after she murdered them. And she seems to at least enjoy their company.
The Hatbox Ghost as a character, as in both iterations, his role is that of a justice-seeking Big Good. Originally, the Bride was a villain, and the HBG provides the punchline that connects her to the head-ghosts in the attic's boxes, and in the new version, he hints to the viewers where some evidence of Constance's crimes may be. Even though he's silent, both times his character exists only to expose the Bride in order bring justice to the Mansion and rid it of its only evil.
A story from the SLG comics titled The Groundskeeper's Secret offers a possible explanation for why the caretaker keeps working at the manor in spite of being scared shitless by the residents: His wife is one of the happy haunts and he spends his break dining with her ghost on her gravesite. He's willing to stick with a job that terrifies him and doesn't earn him much money if it means spending time with someone he loves.
Disney has released a print, which, in addition to forming a skull shape when viewed from afar, depicts the Hatbox Ghost at the end of his long-awaited journey back to the Mansion, arriving at the famous gates.